Binding a digital license to a portable device or the like in a digital rights management (DRM) system and checking out/checking in the digital license to/from the portable device or the like

ABSTRACT

To render digital content encrypted according to a content key (KD) on a first device having a public key (PU 1 ) and a corresponding private key (PR 1 ), a digital license corresponding to the content is obtained, where the digital license includes the content key (KD) therein in an encrypted form. The encrypted content key (KD) from the digital license is decrypted to produce the content key (KD), and the public key (PU 1 ) of the first device is obtained therefrom. The content key (KD) is then encrypted according to the public key (PU 1 ) of the first device (PU 1  (KD)), and a sub-license corresponding to and based on the obtained license is composed, where the sub-license includes (PU 1  (KD)). The composed sub-license is then transferred to the first device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.11/432,276, filed on May 10, 2006, which is a divisional of U.S. patentapplication Ser. No. 09/892,371, filed Jun. 27, 2001, which in turn isrelated to U.S. patent application Ser. No. 09/645,887, filed Aug. 25,2000 and entitled “BINDING DIGITAL CONTENT TO A PORTABLE STORAGE DEVICEOR THE LIKE IN A DIGITAL RIGHTS MANAGEMENT (DRM) SYSTEM”, U.S. patentapplication Ser. No. 09/290,363, filed Apr. 12, 1999 and entitled“ENFORCEMENT ARCHITECTURE AND METHOD FOR DIGITAL RIGHTS MANAGEMENT”, andU.S. Provisional Application No. 60/126,614, filed Mar. 27, 1999 andentitled “ENFORCEMENT ARCHITECTURE AND METHOD FOR DIGITAL RIGHTSMANAGEMENT”, all of which are hereby incorporated by reference in theirentireties.

TECHNICAL FIELD

The present invention relates to an architecture for enforcing rights indigital content. More specifically, the present invention relates tosuch an enforcement architecture that allows access to encrypted digitalcontent only in accordance with parameters specified by license rightsacquired by a user of the digital content.

BACKGROUND OF THE INVENTION

Digital rights management and enforcement is highly desirable inconnection with digital content such as digital audio, digital video,digital text, digital data, digital multimedia, etc., where such digitalcontent is to be distributed to users. Typical modes of distributioninclude tangible devices such as a magnetic (floppy) disk, a magnetictape, an optical (compact) disk (CD), etc., and intangible media such asan electronic bulletin board, an electronic network, the Internet, etc.Upon being received by the user, such user renders or ‘plays’ thedigital content with the aid of an appropriate rendering device such asa media player on a personal computer or the like.

Typically, a content owner or rights-owner, such as an author, apublisher, a broadcaster, etc. (hereinafter “content owner”), wishes todistribute such digital content to a user or recipient in exchange for alicense fee or some other consideration. Such content owner, given thechoice, would likely wish to restrict what the user can do with suchdistributed digital content. For example, the content owner would liketo restrict the user from copying and redistributing such content to asecond user, at least in a manner that denies the content owner alicense fee from such second user.

In addition, the content owner may wish to provide the user with theflexibility to purchase different types of use licenses at differentlicense fees, while at the same time holding the user to the terms ofwhatever type of license is in fact purchased. For example, the contentowner may wish to allow distributed digital content to be played only alimited number of times, only for a certain total time, only on acertain type of machine, only on a certain type of media player, only bya certain type of user, etc.

However, after distribution has occurred, such content owner has verylittle if any control over the digital content. This is especiallyproblematic in view of the fact that practically every new or recentpersonal computer includes the software and hardware necessary to makean exact digital copy of such digital content, and to download suchexact digital copy to a write-able magnetic or optical disk, or to sendsuch exact digital copy over a network such as the Internet to anydestination.

Of course, as part of the legitimate transaction where the license feewas obtained, the content owner may require the user of the digitalcontent to promise not to redistribute such digital content. However,such a promise is easily made and easily broken. A content owner mayattempt to prevent such re-distribution through any of several knownsecurity devices, usually involving encryption and decryption. However,there is likely very little that prevents a mildly determined user fromdecrypting encrypted digital content, saving such digital content in anun-encrypted form, and then re-distributing same.

A need exists, then, for providing an enforcement architecture andmethod that allows the controlled rendering or playing of arbitraryforms of digital content, where such control is flexible and definableby the content owner of such digital content. A need also exists forproviding a controlled rendering environment on a computing device suchas a personal computer, where the rendering environment includes atleast a portion of such enforcement architecture. Such controlledrendering environment allows that the digital content will only berendered as specified by the content owner, even though the digitalcontent is to be rendered on a computing device which is not under thecontrol of the content owner.

Further, a need exists for a trusted component running on the computingdevice, where the trusted component enforces the rights of the contentowner on such computing device in connection with a piece of digitalcontent, even against attempts by the user of such computing device toaccess such digital content in ways not permitted by the content owner.As but one example, such a trusted software component prevents a user ofthe computing device from making a copy of such digital content, exceptas otherwise allowed for by the content owner thereof.

SUMMARY OF THE INVENTION

In the present invention, a method is provided for rendering encrypteddigital content on a first device having a public key (PU1) and acorresponding private key (PR1), where the digital content beingencrypted according to a content key (KD). In the method, a digitallicense corresponding to the content is obtained, where the digitallicense including the content key (KD) therein in an encrypted form. Theencrypted content key (KD) from the digital license is decrypted toproduce the content key (KD), and the public key (PU1) of the firstdevice is obtained therefrom. The content key (KD) is then encryptedaccording to the public key (PU1) of the first device (PU1 (KD)), and asub-license corresponding to and based on the obtained license iscomposed, where the sub-license includes (PU1 (KD)). The composedsub-license is then transferred to the first device, wherein the firstdevice can decrypt (PU1 (KD)) with the private key thereof (PR1) toproduce the content key (KD), and can render the encrypted content onthe first device with the produced content key (KD).

To check out a sub-license from a second device to a first device, thesecond device requests a nonce from the first device, and receives suchnonce. The second device then sends the checked-out sub-license and thereceived nonce to the first device. The first device then concludes thatthe nonce sent by the second device is the same nonce received by thesecond device, and therefore that the sent sub-license that accompaniesthe sent nonce is legitimate, and stores the sent sub-license. To checkin the checked-out sub-license, the first device deletes the checked-outsub-license and then provides a trusted indication to the second devicethat the checked-out sub-license has in fact been deleted.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe embodiments of the present invention, will be better understood whenread in conjunction with the appended drawings. For the purpose ofillustrating the invention, there are shown in the drawings embodimentswhich are presently preferred. As should be understood, however, theinvention is not limited to the precise arrangements andinstrumentalities shown. In the drawings:

FIG. 1 is a block diagram showing an enforcement architecture inaccordance with one embodiment of the present invention;

FIG. 2 is a block diagram of the authoring tool of the architecture ofFIG. 1 in accordance with one embodiment of the present invention;

FIG. 3 is a block diagram of a digital content package having digitalcontent for use in connection with the architecture of FIG. 1 inaccordance with one embodiment of the present invention;

FIG. 4 is a block diagram of the users computing device of FIG. 1 inaccordance with one embodiment of the present invention;

FIGS. 5A and 5B are flow diagrams showing the steps performed inconnection with the Digital Rights Management (DRM) system of thecomputing device of FIG. 4 to render content in accordance with oneembodiment of the present invention;

FIG. 6 is a flow diagram showing the steps performed in connection withthe DRM system of FIG. 4 to determine whether any valid, enablinglicenses are present in accordance with one embodiment of the presentinvention;

FIG. 7 is a flow diagram showing the steps performed in connection withthe DRM system of FIG. 4 to obtain a license in accordance with oneembodiment of the present invention;

FIG. 8 is a block diagram of a digital license for use in connectionwith the architecture of FIG. 1 in accordance with one embodiment of thepresent invention;

FIG. 9 is a flow diagram showing the steps performed in connection withthe DRM system of FIG. 4 to obtain a new black box in accordance withone embodiment of the present invention;

FIG. 10 is a flow diagram showing the key transaction steps performed inconnection with the DRM system of FIG. 4 to validate a license and apiece of digital content and render the content in accordance with oneembodiment of the present invention;

FIG. 11 is a block diagram showing the license evaluator of FIG. 4 alongwith a Digital Rights License (DRL) of a license and a language enginefor interpreting the DRL in accordance with one embodiment of thepresent invention;

FIG. 12 is a block diagram representing a general purpose computersystem in which aspects of the present invention and/or portions thereofmay be incorporated;

FIG. 13 is a block diagram representing an arrangement wherein aportable device couples to a computer for purposes of downloadingcontent and a corresponding sub-license in accordance with oneembodiment of the present invention;

FIGS. 14 and 14A are flow diagrams showing steps performed in deliveringdigital content and a sub-license from the computer to the portabledevice of FIG. 13 in accordance with one embodiment of the presentinvention;

FIG. 15 is a block diagram showing a license and a sub-license derivedfrom the license in the manner shown in FIG. 14 in accordance with oneembodiment of the present invention;

FIG. 16 is a flow diagram showing steps performed by the portable deviceof FIG. 13 in rendering content based on a sub-license in accordancewith one embodiment of the present invention; and

FIG. 17 is a flow diagram showing steps performed by the computer andthe portable device of FIG. 13 to check out and check in a sub-licensein accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings in details, wherein like numerals are used toindicate like elements throughout, there is shown in FIG. 1 anenforcement architecture 10 in accordance with one embodiment of thepresent invention. Overall, the enforcement architecture 10 allows anowner of digital content 12 to specify license rules that must besatisfied before such digital content 12 is allowed to be rendered on auser's computing device 14. Such license rules are embodied within adigital license 16 that the user/user's computing device 14(hereinafter, such terms are interchangeable unless circumstancesrequire otherwise) must obtain from the content owner or an agentthereof. The digital content 12 is distributed in an encrypted form, andmay be distributed freely and widely. Preferably, the decrypting key(KD) for decrypting the digital content 12 is included with the license16.

Computer Environment

FIG. 12 and the following discussion are intended to provide a briefgeneral description of a suitable computing environment in which thepresent invention and/or portions thereof may be implemented. Althoughnot required, the invention is described in the general context ofcomputer-executable instructions, such as program modules, beingexecuted by a computer, such as a client workstation or a server.Generally, program modules include routines, programs, objects,components, data structures and the like that perform particular tasksor implement particular abstract data types. Moreover, it should beappreciated that the invention and/or portions thereof may be practicedwith other computer system configurations, including hand-held devices,multi-processor systems, microprocessor-based or programmable consumerelectronics, network PCs, minicomputers, mainframe computers and thelike. The invention may also be practiced in distributed computingenvironments where tasks are performed by remote processing devices thatare linked through a communications network. In a distributed computingenvironment, program modules may be located in both local and remotememory storage devices.

As shown in FIG. 12, an exemplary general purpose computing systemincludes a conventional personal computer 120 or the like, including aprocessing unit 121, a system memory 122, and a system bus 123 thatcouples various system components including the system memory to theprocessing unit 121. The system bus 123 may be any of several types ofbus structures including a memory bus or memory controller, a peripheralbus, and a local bus using any of a variety of bus architectures. Thesystem memory includes read-only memory (ROM) 124 and random accessmemory (RAM) 125. A basic input/output system 126 (BIOS), containing thebasic routines that help to transfer information between elements withinthe personal computer 120, such as during start-up, is stored in ROM124.

The personal computer 120 may further include a hard disk drive 127 forreading from and writing to a hard disk (not shown), a magnetic diskdrive 128 for reading from or writing to a removable magnetic disk 129,and an optical disk drive 130 for reading from or writing to a removableoptical disk 131 such as a CD-ROM or other optical media. The hard diskdrive 127, magnetic disk drive 128, and optical disk drive 130 areconnected to the system bus 123 by a hard disk drive interface 132, amagnetic disk drive interface 133, and an optical drive interface 134,respectively. The drives and their associated computer-readable mediaprovide non-volatile storage of computer readable instructions, datastructures, program modules and other data for the personal computer120.

Although the exemplary environment described herein employs a hard disk,a removable magnetic disk 129, and a removable optical disk 131, itshould be appreciated that other types of computer readable media whichcan store data that is accessible by a computer may also be used in theexemplary operating environment. Such other types of media include amagnetic cassette, a flash memory card, a digital video disk, aBernoulli cartridge, a random access memory (RAM), a read-only memory(ROM), and the like.

A number of program modules may be stored on the hard disk, magneticdisk 129, optical disk 131, ROM 124 or RAM 125, including an operatingsystem 135, one or more application programs 136, other program modules137 and program data 138. A user may enter commands and information intothe personal computer 120 through input devices such as a keyboard 140and pointing device 142. Other input devices (not shown) may include amicrophone, joystick, game pad, satellite disk, scanner, or the like.These and other input devices are often connected to the processing unit121 through a serial port interface 146 that is coupled to the systembus, but may be connected by other interfaces, such as a parallel port,game port, or universal serial bus (USB). A monitor 147 or other type ofdisplay device is also connected to the system bus 123 via an interface,such as a video adapter 148. In addition to the monitor 147, a personalcomputer typically includes other peripheral output devices (not shown),such as speakers and printers. The exemplary system of FIG. 12 alsoincludes a host adapter 155, a Small Computer System Interface (SCSI)bus 156, and an external storage device 162 connected to the SCSI bus156.

The personal computer 120 may operate in a networked environment usinglogical connections to one or more remote computers, such as a remotecomputer 149. The remote computer 149 may be another personal computer,a server, a router, a network PC, a peer device or other common networknode, and typically includes many or all of the elements described aboverelative to the personal computer 120, although only a memory storagedevice 150 has been illustrated in FIG. 12. The logical connectionsdepicted in FIG. 12 include a local area network (LAN) 151 and a widearea network (WAN) 152. Such networking environments are commonplace inoffices, enterprise-wide computer networks, intranets, and the Internet.

When used in a LAN networking environment, the personal computer 120 isconnected to the LAN 151 through a network interface or adapter 153.When used in a WAN networking environment, the personal computer 120typically includes a modem 154 or other means for establishingcommunications over the wide area network 152, such as the Internet. Themodem 154, which may be internal or external, is connected to the systembus 123 via the serial port interface 146. In a networked environment,program modules depicted relative to the personal computer 120, orportions thereof, may be stored in the remote memory storage device. Itwill be appreciated that the network connections shown are exemplary andother means of establishing a communications link between the computersmay be used.

Architecture

Referring again to FIG. 1, in one embodiment of the present invention,the architecture 10 includes an authoring tool 18, a content-keydatabase 20, a content server 22, a license server 24, and a black boxserver 26, as well as the aforementioned users computing device 14.

Architecture—Authoring Tool 18

The authoring tool 18 is employed by a content owner to package a pieceof digital content 12 into a form that is amenable for use in connectionwith the architecture 10 of the present invention. In particular, thecontent owner provides the authoring tool 18 with the digital content12, instructions and/or rules that are to accompany the digital content12, and instructions and/or rules as to how the digital content 12 is tobe packaged. The authoring tool 18 then produces a digital contentpackage 12 p having the digital content 12 encrypted according to anencryption/decryption key, and the instructions and/or rules thataccompany the digital content 12.

In one embodiment of the present invention, the authoring tool 18 isinstructed to serially produce several different digital content 12packages 12 p, each having the same digital content 12 encryptedaccording to a different encryption/decryption key. As should beunderstood, having several different packages 12 p with the same digitalcontent 12 may be useful for tracking the distribution of such packages12 p/content 12 (hereinafter simply “digital content 12”, unlesscircumstances require otherwise). Such distribution tracking is notordinarily necessary, but may be used by an investigative authority incases where the digital content 12 has been illegally sold or broadcast.

In one embodiment of the present invention, the encryption/decryptionkey that encrypts the digital content 12 is a symmetric key, in that theencryption key is also the decryption key (KD). As will be discussedbelow in more detail, such decryption key (KD) is delivered to a user'scomputing device 14 in a hidden form as part of a license 16 for suchdigital content 12. Preferably, each piece of digital content 12 isprovided with a content ID (or each package 12 p is provided with apackage ID), each decryption key (KD) has a key ID, and the authoringtool 18 causes the decryption key (KD), key ID, and content ID (orpackage ID) for each piece of digital content 12 (or each package 12 p)to be stored in the content-key database 20. In addition, license dataregarding the types of licenses 16 to be issued for the digital content12 and the terms and conditions for each type of license 16 may bestored in the content-key database 20, or else in another database (notshown). Preferably, the license data can be modified by the contentowner at a later time as circumstances and market conditions mayrequire.

In use, the authoring tool 18 is supplied with information including,among other things:

-   -   the digital content 12 to be packaged;    -   the type and parameters of watermarking and/or fingerprinting to        be employed, if any;    -   the type and parameters of data compression to be employed, if        any;    -   the type and parameters of encryption to be employed;    -   the type and parameters of serialization to be employed, if any;        and    -   the instructions and/or rules that are to accompany the digital        content 12.

As is known, a watermark is a hidden, computer-readable signal that isadded to the digital content 12 as an identifier. A fingerprint is awatermark that is different for each instance. As should be understood,an instance is a version of the digital content 12 that is unique.Multiple copies of any instance may be made, and any copy is of aparticular instance. When a specific instance of digital content 12 isillegally sold or broadcast, an investigative authority can perhapsidentify suspects according to the watermark/fingerprint added to suchdigital content 12.

Data compression may be performed according to any appropriatecompression algorithm without departing from the spirit and scope of thepresent invention. For example, the .mp3 or .wav compression algorithmmay be employed. Of course, the digital content 12 may already be in acompressed state, in which case no additional compression is necessary.

The instructions and/or rules that are to accompany the digital content12 may include practically any appropriate instructions, rules, or otherinformation without departing from the spirit and scope of the presentinvention. As will be discussed below, such accompanyinginstructions/rules/information are primarily employed by the user andthe user's computing device 14 to obtain a license 16 to render thedigital content 12. Accordingly, such accompanyinginstructions/rules/information may include an appropriately formattedlicense acquisition script or the like, as will be described in moredetail below. In addition, or in the alternative, such accompanyinginstructions/rules/information may include ‘preview’ informationdesigned to provide a user with a preview of the digital content 12.

With the supplied information, the authoring tool 18 then produces oneor more packages 12 p corresponding to the digital content 12. Eachpackage 12 p may then be stored on the content server 22 fordistribution to the world.

In one embodiment of the present invention, and referring now to FIG. 2,the authoring tool 18 is a dynamic authoring tool 18 that receives inputparameters which can be specified and operated on. Accordingly, suchauthoring tool 18 can rapidly produce multiple variations of package 12p for multiple pieces of digital content 12. Preferably, the inputparameters are embodied in the form of a dictionary 28, as shown, wherethe dictionary 28 includes such parameters as:

-   -   the name of the input file 29 a having the digital content 12;    -   the type of encoding that is to take place    -   the encryption/decryption key (KD) to be employed,    -   the accompanying instructions/rules/information (‘header        information’) to be packaged with the digital content 12 in the        package 12 p.    -   the type of muxing that is to occur; and    -   the name of the output file 29 b to which the package 12 p based        on the digital content 12 is to be written.

As should be understood, such dictionary 28 is easily and quicklymodifiable by an operator of the authoring tool 18 (human or machine),and therefore the type of authoring performed by the authoring tool 18is likewise easily and quickly modifiable in a dynamic manner. In oneembodiment of the present invention, the authoring tool 18 includes anoperator interface (not shown) displayable on a computer screen to ahuman operator. Accordingly, such operator may modify the dictionary 28by way of the interface, and further may be appropriately aided and/orrestricted in modifying the dictionary 28 by way of the interface.

In the authoring tool 18, and as seen in FIG. 2, a source filter 18 areceives the name of the input file 29 a having the digital content 12from the dictionary 28, and retrieves such digital content 12 from suchinput file and places the digital content 12 into a memory 29 c such asa RAM or the like. An encoding filter 18 b then performs encoding on thedigital content 12 in the memory 29 c to transfer the file from theinput format to the output format according to the type of encodingspecified in the dictionary 28 (i.e., .wav to .asp, .mp3 to asp, etc.),and places the encoded digital content 12 in the memory 29 c. As shown,the digital content 12 to be packaged (music, e.g.) is received in acompressed format such as the .wav or .mp3 format, and is transformedinto a format such as the asp (active streaming protocol) format. Ofcourse, other input and output formats may be employed without departingfrom the spirit and scope of the present invention.

Thereafter, an encryption filter 18 c encrypts the encoded digitalcontent 12 in the memory 29 c according to the encryption/decryption key(KD) specified in the dictionary 28, and places the encrypted digitalcontent 12 in the memory 29 c. A header filter 18 d then adds the headerinformation specified in the dictionary 28 to the encrypted digitalcontent 12 in the memory 29 c.

As should be understood, depending on the situation, the package 12 pmay include multiple streams of temporally aligned digital content 12(one stream being shown in FIG. 2), where such multiple streams aremultiplexed (i.e., ‘muxed’). Accordingly, a mux filter 18 e performsmuxing on the header information and encrypted digital content 12 in thememory 29 c according to the type of muxing specified in the dictionary28, and places the result in the memory 29 c. A file writer filter 18 fthen retrieves the result from the memory 29 c and writes such result tothe output file 29 b specified in the dictionary 28 as the package 12 p.

It should be noted that in certain circumstances, the type of encodingto be performed will not normally change. Since the type of muxingtypically is based on the type of encoding, it is likewise the case thatthe type of muxing will not normally change, either. If this is in factthe case, the dictionary 28 need not include parameters on the type ofencoding and/or the type of muxing. Instead, it is only necessary thatthe type of encoding be ‘hardwired’ into the encoding filter and/or thatthe type of muxing be ‘hardwired’ into the mux filter. Of course, ascircumstance require, the authoring tool 18 may not include all of theaforementioned filters, or may include other filters, and any includedfilter may be hardwired or may perform its function according toparameters specified in the dictionary 28, all without departing fromthe spirit and scope of the present invention.

Preferably, the authoring tool 18 is implemented on an appropriatecomputer, processor, or other computing machine by way of appropriatesoftware. The structure and operation of such machine and such softwareshould be apparent based on the disclosure herein and therefore do notrequire any detailed discussion in the present disclosure.

Architecture—Content Server 22

Referring again to FIG. 1, in one embodiment of the present invention,the content server 22 distributes or otherwise makes available forretrieval the packages 12 p produced by the authoring tool 18. Suchpackages 12 p may be distributed as requested by the content server 22by way of any appropriate distribution channel without departing fromthe spirit and scope of the present invention. For example, suchdistribution channel may be the Internet or another network, anelectronic bulletin board, electronic mail, or the like. In addition,the content server 22 may be employed to copy the packages 12 p ontomagnetic or optical disks or other storage devices, and such storagedevices may then be distributed.

It will be appreciated that the content server 22 distributes packages12 p without regard to any trust or security issues. As discussed below,such issues are dealt with in connection with the license server 24 andthe relationship between such license server 24 and the user's computingdevice 14. In one embodiment of the present invention, the contentserver 22 freely releases and distributes packages 12 p having digitalcontent 12 to any distributes requesting same. However, the contentserver 22 may also release and distribute such packages 12 p in arestricted manner without departing from the spirit and scope of thepresent invention. For example, the content server 22 may first requirepayment of a pre-determined distribution fee prior to distribution, ormay require that a distributes identify itself, or may indeed make adetermination of whether distribution is to occur based on anidentification of the distributee.

In addition, the content server 22 may be employed to perform inventorymanagement by controlling the authoring tool 18 to generate a number ofdifferent packages 12 p in advance to meet an anticipated demand. Forexample, the server could generate 100 packages 12 p based on the samedigital content 12, and serve each package 12 p 10 times. As supplies ofpackages 12 p dwindle to 20, for example, the content server 22 may thendirect the authoring tool 18 to generate 80 additional packages 12 p,again for example.

Preferably, the content server 22 in the architecture 10 has a uniquepublic/private key pair (PU-CS, PR-CS) that is employed as part of theprocess of evaluating a license 16 and obtaining a decryption key (KD)for decrypting corresponding digital content 12, as will be explained inmore detail below. As is known, a public/private key pair is anasymmetric key, in that what is encrypted in one of the keys in the keypair can only be decrypted by the other of the keys in the key pair. Ina public/private key pair encryption system, the public key may be madeknown to the world, but the private key should always be held inconfidence by the owner of such private key. Accordingly, if the contentserver 22 encrypts data with its private key (PR-CS), it can send theencrypted data out into the world with its public key (PU-CS) fordecryption purposes. Correspondingly, if an external device wants tosend data to the content server 22 so that only such content server 22can decrypt such data, such external device must first obtain the publickey of the content server 22 (PU-CS) and then must encrypt the data withsuch public key. Accordingly, the content server 22 (and only thecontent server 22) can then employ its private key (PR-CS) to decryptsuch encrypted data.

As with the authoring tool 18, the content server 22 is implemented onan appropriate computer, processor, or other computing machine by way ofappropriate software. The structure and operation of such machine andsuch software should be apparent based on the disclosure herein andtherefore do not require any detailed discussion in the presentdisclosure. Moreover, in one embodiment of the present invention, theauthoring tool 18 and the content server 22 may reside on a singlecomputer, processor, or other computing machine, each in a separate workspace. It should be recognized, moreover, that the content server 22 mayin certain circumstances include the authoring tool 18 and/or performthe functions of the authoring tool 18, as discussed above.

Structure of Digital Content Package 12 p

Referring now to FIG. 3, in one embodiment of the present invention, thedigital content package 12 p as distributed by the content server 22includes:

-   -   the digital content 12 encrypted with the encryption/decryption        key (KD), as was discussed above (i.e., (KD(CONTENT)));    -   the content ID (or package ID) of such digital content 12 (or        package 12 p);    -   the key ID of the decryption key (KD);    -   license acquisition information, preferably in an un-encrypted        form; and    -   the key KD encrypting the content server 22 public key (PU-CS),        signed by the content server 22 private key (PR-CS) (i.e., (KD        (PU-CS) S (PR-CS))).

With regard to (KD (PU-CS) S (PR-CS)), it is to be understood that suchitem is to be used in connection with validating the digital content 12and/or package 12 p, as will be explained below. Unlike a certificatewith a digital signature (see below), the key (PU-CS) is not necessaryto get at (KD (PU-CS)). Instead, the key (PU-CS) is obtained merely byapplying the decryption key (KD). Once so obtained, such key (PU-CS) maybe employed to test the validity of the signature (S (PR-CS)).

It should also be understood that for such package 12 p to beconstructed by the authoring tool 18, such authoring tool 18 mustalready possess the license acquisition information and (KC) (PU-CS) S(PR-CS)), presumably as header information supplied by the dictionary28. Moreover, the authoring tool 18 and the content server 22 mustpresumably interact to construct (KD (PU-CS) S (PR-CS)). Suchinteraction may for example include the steps of:

-   -   the content server 22 sending (PU-CS) to the authoring tool 18;    -   the authoring tool 18 encrypting (PU-CS) with (KD) to produce        (KD (PU-CS));    -   the authoring tool 18 sending (KD (PU-CS)) to the content server        22;    -   the content server 22 signing (KD (PU-CS)) with (PR-CS) to        produce (KD (PU-CS) S (PR-CS)); and    -   the content server 22 sending (KD (PU-CS) S (PR-CS)) to the        authoring tool 18.        Architecture—License Server 24

Referring again to FIG. 1, in one embodiment of the present invention,the license server 24 performs the functions of receiving a request fora license 16 from a user's computing device 14 in connection with apiece of digital content 12, determining whether the users computingdevice 14 can be trusted to honor an issued license 16, negotiating sucha license 16, constructing such license 16, and transmitting suchlicense 16 to the users computing device 14. Preferably, suchtransmitted license 16 includes the decryption key (KD) for decryptingthe digital content 12. Such license server 24 and such functions willbe explained in more detail below. Preferably, and like the contentserver 22, the license server 24 in the architecture 10 has a uniquepublic/private key pair (PU-LS, PR-LS) that is employed as part of theprocess of evaluating a license 16 and obtaining a decryption key (KD)for decrypting corresponding digital content 12, as will be explained inmore detail below.

As with the authoring tool 18 and the content server 22, the licenseserver 24 is implemented on an appropriate computer, processor, or othercomputing machine by way of appropriate software. The structure andoperation of such machine and such software should be apparent based onthe disclosure herein and therefore do not require any detaileddiscussion in the present disclosure. Moreover, in one embodiment of thepresent invention the authoring tool 18 and/or the content server 22 mayreside on a single computer, processor, or other computing machinetogether with the license server 24, each in a separate work space.

In one embodiment of the present invention, prior to issuance of alicense 16, the license server 24 and the content server 22 enter intoan agency agreement or the like, wherein the license server 24 in effectagrees to be the licensing authority for at least a portion of thedigital content 12 distributed by the content server 22. As should beunderstood, one content server 22 may enter into an agency agreement orthe like with several license servers 24, and/or one license server 24may enter into an agency agreement or the like with several contentservers 22, all without departing from the spirit and scope of thepresent invention.

Preferably, the license server 24 can show to the world that it does infact have the authority to issue a license 16 for digital content 12distributed by the content server 22. To do so, it is preferable thatthe license server 24 send to the content server 22 the license server24 public key (PU-LS), and that the content server 22 then send to thelicense server 24 a digital certificate containing PU-LS as the contentssigned by the content server 22 private key (CERT (PU-LS) S (PR-CS)). Asshould be understood, the contents (PU-LS) in such certificate can onlybe accessed with the content server 22 public key (PU-CS). As shouldalso be understood, in general, a digital signature of underlying datais an encrypted form of such data, and will not match such data whendecrypted if such data has been adulterated or otherwise modified.

As a licensing authority in connection with a piece of digital content12, and as part of the licensing function, the license server 24 musthave access to the decryption key (KD) for such digital content 12.Accordingly, it is preferable that license server 24 have access to thecontent-key database 20 that has the decryption key (KD), key ID, andcontent ID (or package ID) for such digital content 12 (or package 12p).

Architecture—Black Box Server 26

Still referring to FIG. 1, in one embodiment of the present invention,the black box server 26 performs the functions of installing and/orupgrading a new black box 30 in a users computing device 14. As will beexplained in more detail below, the black box 30 performs encryption anddecryption functions for the user's computing device 14. As will also beexplained in more detail below, the black box 30 is intended to besecure and protected from attack. Such security and protection isprovided, at least in part, by upgrading the black box 30 to a newversion as necessary by way of the black box server 26, as will beexplained in more detail below.

As with the authoring tool 18, the content server 22, and the licenseserver 24, the black box server 26 is implemented on an appropriatecomputer, processor, or other computing machine by way of appropriatesoftware. The structure and operation of such machine and such softwareshould be apparent based on the disclosure herein and therefore do notrequire any detailed discussion in the present disclosure. Moreover, inone embodiment of the present invention the license server 24, theauthoring tool 18, and/or the content server 22 may reside on a singlecomputer, processor, or other computing machine together with the blackbox server 26, each in a separate work space. Note, though, that forsecurity purposes, it may be wise to have the black box server 26 on aseparate machine.

Architecture—User's Computing Device 14

Referring now to FIG. 4, in one embodiment of the present invention, theusers computing device 14 is a personal computer or the like, havingelements including a keyboard, a mouse, a screen, a processor, RAM, ROM,a hard drive, a floppy drive, a CD player, and/or the like. However, theuser's computing device 14 may also be a dedicated viewing device suchas a television or monitor, a dedicated audio device such as a stereo orother music player, a dedicated printer, or the like, among otherthings, all without departing from the spirit and scope of the presentinvention.

The content owner for a piece of digital content 12 must trust that theuser's computing device 14 will abide by the rules specified by suchcontent owner, i.e. that the digital content 12 will not be renderedunless the user obtains a license 16 that permits the rendering in themanner sought. Preferably, then, the user's computing device 14 mustprovide a trusted component or mechanism 32 that can satisfy to thecontent owner that such computing device 14 will not render the digitalcontent 12 except according to the license rules embodied in the license16 associated with the digital content 12 and obtained by the user.

Here, the trusted mechanism 32 is a Digital Rights Management (DRM)system 32 that is enabled when a user requests that a piece of digitalcontent 12 be rendered, that determines whether the user has a license16 to render the digital content 12 in the manner sought, thateffectuates obtaining such a license 16 if necessary, that determineswhether the user has the right to play the digital content 12 accordingto the license 16, and that decrypts the digital content 12 forrendering purposes if in fact the user has such right according to suchlicense 16. The contents and function of the DRM system 32 on the user'scomputing device 14 and in connection with the architecture 10 aredescribed below.

DRM System 32

The DRM system 32 performs four main functions with the architecture 10disclosed herein: (1) content acquisition, (2) license acquisition, (3)content rendering, and (4) black box 30 installation/update. Preferably,any of the functions can be performed at any time, although it isrecognized that some of the functions already require that digitalcontent 12 be acquired.

DRM System 32—Content Acquisition

Acquisition of digital content 12 by a user and/or the users computingdevice 14 is typically a relatively straight-forward matter andgenerally involves placing a file having encrypted digital content 12 onthe user's computing device 14. Of course, to work with the architecture10 and the DRM system 32 disclosed herein, it is necessary that theencrypted digital content 12 be in a form that is amenable to sucharchitecture 10 and DRM system 32, such as the digital package 12 p aswill be described below.

As should be understood, the digital content 12 may be obtained in anymanner from a content server 22, either directly or indirectly, withoutdeparting from the spirit and scope of the present invention. Forexample, such digital content 12 may be downloaded from a network suchas the Internet, located on an obtained optical or magnetic disk or thelike, received as part of an E-mail message or the like, or downloadedfrom an electronic bulletin board or the like.

Such digital content 12, once obtained, is preferably stored in a mannersuch that the obtained digital content 12 is accessible by a renderingapplication 34 (to be described below) running on the computing device14, and by the DRM system 32. For example, the digital content 12 may beplaced as a file on a hard drive (not shown) of the users computingdevice 14, or on a network server (not shown) accessible to thecomputing device 14. In the case where the digital content 12 isobtained on an optical or magnetic disk or the like, it may only benecessary that such disk be present in an appropriate drive (not shown)coupled to the user's computing device 14.

In the present invention, it is not envisioned that any special toolsare necessary to acquire digital content 12, either from the contentserver 22 as a direct distribution source or from some intermediary asan indirect distribution source. That is, it is preferable that digitalcontent 12 be as easily acquired as any other data file. However, theDRM system 32 and/or the rendering application 34 may include aninterface (not shown) designed to assist the user in obtaining digitalcontent 12. For example, the interface may include a web browserespecially designed to search for digital content 12, links topre-defined Internet web sites that are known to be sources of digitalcontent 12, and the like.

DRM System 32—Content Rendering, Part 1

Referring now to FIG. 5A, in one embodiment of the present invention,assuming the encrypted digital content 12 has been distributed to andreceived by a user and placed by the user on the computing device 14 inthe form of a stored file, the user will attempt to render the digitalcontent 12 by executing some variation on a render command (step 501).For example, such render command may be embodied as a request to ‘play’or ‘open’ the digital content 12. In some computing environments, suchas for example the “MICROSOFT WINDOWS” operating system, distributed byMICROSOFT Corporation of Redmond, Wash., such play or open command maybe as simple as ‘clicking’ on an icon representative of the digitalcontent 12. Of course, other embodiments of such render command may beemployed without departing from the spirit and scope of the presentinvention. In general, such render command may be considered to beexecuted whenever a user directs that a file having digital content 12be opened, run, executed, and/or the like.

Importantly, and in addition, such render command may be embodied as arequest to copy the digital content 12 to another form, such as to aprinted form, a visual form, an audio form; etc. As should beunderstood, the same digital content 12 may be rendered in one form,such as on a computer screen, and then in another form, such as aprinted document. In the present invention, each type of rendering isperformed only if the user has the right to do so, as will be explainedbelow.

In one embodiment of the present invention, the digital content 12 is inthe form of a digital file having a file name ending with an extension,and the computing device 14 can determine based on such extension tostart a particular kind of rendering application 34. For example, if thefile name extension indicates that the digital content 12 is a textfile, the rendering application 34 is some form of word processor suchas the “MICROSOFT WORD”, distributed by MICROSOFT Corporation ofRedmond, Wash. Likewise, if the file name extension indicates that thedigital content 12 is an audio, video, and/or multimedia file, therendering application 34 is some form of multimedia player, such as“MICROSOFT MEDIA PLAYER”, also distributed by MICROSOFT Corporation ofRedmond, Wash.

Of course, other methods of determining a rendering application may beemployed without departing from the spirit and scope of the presentinvention. As but one example, the digital content 12 may containmeta-data in an un-encrypted form (i.e., the aforementioned headerinformation), where the meta-data includes information on the type ofrendering application 34 necessary to render such digital content 12.

Preferably, such rendering application 34 examines the digital content12 associated with the file name and determines whether such digitalcontent 12 is encrypted in a rights-protected form (steps 503, 505). Ifnot protected, the digital content 12 may be rendered without furtherado (step 507). If protected, the rendering application 34 determinesfrom the encrypted digital content 12 that the DRM system 32 isnecessary to play such digital content 12. Accordingly, such renderingapplication 34 directs the user's computing device 14 to run the DRMsystem 32 thereon (step 509). Such rendering application 34 then callssuch DRM system 32 to decrypt the digital content 12 (step 511). As willbe discussed in more detail below, the DRM system 32 in fact decryptsthe digital content 12 only if the user has a valid license 16 for suchdigital content 12 and the right to play the digital content 12according to the license rules in the valid license 16. Preferably, oncethe DRM system 32 has been called by the rendering application 34, suchDRM system 32 assumes control from the rendering application 34, atleast for purposes of determining whether the user has a right to playsuch digital content 12 (step 513).

DRM System 32 Components

In one embodiment of the present invention, and referring again to FIG.4, the DRM system 32 includes a license evaluator 36, the black box 30,a license store 38, and a state store 40.

DRM System 32 Components—License Evaluator 36

The license evaluator 36 locates one or more licenses 16 that correspondto the requested digital content 12, determines whether such licenses 16are valid, reviews the license rules in such valid licenses 16, anddetermines based on the reviewed license rules whether the requestinguser has the right to render the requested digital content 12 in themanner sought, among other things. As should be understood, the licenseevaluator 36 is a trusted component in the DRM system 32. In the presentdisclosure, to be ‘trusted’ means that the license server 24 (or anyother trusting element) is satisfied that the trusted element will carryout the wishes of the owner of the digital content 12 according to therights description in the license 16, and that a user cannot easilyalter such trusted element for any purpose, nefarious or otherwise.

The license evaluator 36 has to be trusted in order to ensure that suchlicense evaluator 36 will in fact evaluate a license 16 properly, and toensure that such license evaluator 36 has not been adulterated orotherwise modified by a user for the purpose of bypassing actualevaluation of a license 16. Accordingly, the license evaluator 36 is runin a protected or shrouded environment such that the user is deniedaccess to such license evaluator 36. Other protective measures may ofcourse be employed in connection with the license evaluator 36 withoutdeparting from the spirit and scope of the present invention.

DRM System 32 Components—Black Box 30

Primarily, and as was discussed above, the black box 30 performsencryption and decryption functions in the DRM system 32. In particular,the black box 30 works in conjunction with the license evaluator 36 todecrypt and encrypt certain information as part of the licenseevaluation function. In addition, once the license evaluator 36determines that a user does in fact have the right to render therequested digital content 12 in the manner sought, the black box 30 isprovided with a decryption key (KD) for such digital content 12, andperforms the function of decrypting such digital content 12 based onsuch decryption key (KD).

The black box 30 is also a trusted component in the DRM system 32. Inparticular, the license server 24 must trust that the black box 30 willperform the decryption function only in accordance with the licenserules in the license 16, and also trust that such black box 30 will notoperate should it become adulterated or otherwise modified by a user forthe nefarious purpose of bypassing actual evaluation of a license 16.Accordingly, the black box 30 is also run in a protected or shroudedenvironment such that the user is denied access to such black box 30.Again, other protective measures may be employed in connection with theblack box 30 without departing from the spirit and scope of the presentinvention. Preferably, and like the content server 22 and license server24, the black box 30 in the DRM system 32 has a unique public/privatekey pair (PU-BB, PR-BB) that is employed as part of the process ofevaluating the license 16 and obtaining a decryption key (KD) fordecrypting the digital content 12, as will be described in more detailbelow.

DRM System 32 Components—License Store 38

The license store 38 stores licenses 16 received by the DRM system 32for corresponding digital content 12. The license store 38 itself neednot be trusted since the license store 38 merely stores licenses 16,each of which already has trust components built thereinto, as will bedescribed below. In one embodiment of the present invention, the licensestore 38 is merely a sub-directory of a drive such as a hard disk driveor a network drive. However, the license store 38 may be embodied in anyother form without departing from the spirit and scope of the presentinvention, so long as such license store 38 performs the function ofstoring licenses 16 in a location relatively convenient to the DRMsystem 32.

DRM System 32 Components—State Store 40

The state store 40 performs the function of maintaining stateinformation corresponding to licenses 16 presently or formerly in thelicense store 38. Such state information is created by the DRM system 32and stored in the state store 40 as necessary. For example, if aparticular license 16 only allows a pre-determined number of renderingsof a piece of corresponding digital content 12, the state store 40maintains state information on how many renderings have in fact takenplace in connection with such license 16. The state store 40 continuesto maintain state information on licenses 16 that are no longer in thelicense store 38 to avoid the situation where it would otherwise beadvantageous to delete a license 16 from the license store 38 and thenobtain an identical license 16 in an attempt to delete the correspondingstate information from the state store 40.

The state store 40 also has to be trusted in order to ensure that theinformation stored therein is not reset to a state more favorable to auser. Accordingly, the state store 40 is likewise run in a protected orshrouded environment such that the user is denied access to such statestore 40. Once again, other protective measures may of course beemployed in connection with the state store 40 without departing fromthe spirit and scope of the present invention. For example, the statestore 40 may be stored by the DRM system 32 on the computing device 14in an encrypted form.

DRM System 32—Content Rendering, Part 2

Referring again to FIG. 5A, and again discussing content rendering inone embodiment of the present invention, once the DRM system 32 hasassumed control from the calling rendering application 34, such DRMsystem 32 then begins the process of determining whether the user has aright to render the requested digital content 12 in the manner sought.In particular, the DRM system 32 either locates a valid, enablinglicense 16 in the license store (steps 515, 517) or attempts to acquirea valid, enabling license 16 from the license server 24 (i.e. performsthe license acquisition function as discussed below and as shown in FIG.7).

As a first step, and referring now to FIG. 6, the license evaluator 36of such DRM system 32 checks the license store 38 for the presence ofone or more received licenses 16 that correspond to the digital content12 (step 601). Typically, the license 16 is in the form of a digitalfile, as will be discussed below, although it will be recognized thatthe license 16 may also be in other forms without departing from thespirit and scope of the present invention. Typically, the user willreceive the digital content 12 without such license 16, although it willlikewise be recognized that the digital content 12 may be received witha corresponding license 16 without departing from the spirit and scopeof the present invention.

As was discussed above in connection with FIG. 3, each piece of digitalcontent 12 is in a package 12 p with a content ID (or package ID)identifying such digital content 12 (or package 12 p), and a key IDidentifying the decryption key (KD) that will decrypt the encrypteddigital content 12. Preferably, the content ID (or package ID) and thekey ID are in an unencrypted form. Accordingly, and in particular, basedon the content ID of the digital content 12, the license evaluator 36looks for any license 16 in the license store 38 that contains anidentification of applicability to such content ID. Note that multiplesuch licenses 16 may be found, especially if the owner of the digitalcontent 12 has specified several different kinds of licenses 16 for suchdigital content 12, and the user has obtained multiple ones of suchlicenses 16. If in fact the license evaluator 36 does not find in thelicense store 38 any license 16 corresponding to the requested digitalcontent 12, the DRM system 32 may then perform the function of licenseacquisition (step 519 of FIG. 5), to be described below.

Assume now that the DRM system 32 has been requested to render a pieceof digital content 12, and one or more licenses 16 corresponding theretoare present in the license store 38. In one embodiment of the presentinvention, then, the license evaluator 36 of the DRM system 32 proceedsto determine for each such license 16 whether such license 16 itself isvalid (steps 603 and 605 of FIG. 6). Preferably, and in particular, eachlicense 16 includes a digital signature 26 based on the content 28 ofthe license 16. As should be understood, the digital signature 26 willnot match the license 16 if the content 28 has been adulterated orotherwise modified. Thus, the license evaluator 36 can determine basedon the digital signature 26 whether the content 28 is in the form thatit was received from the license server 24 (i.e., is valid). If no validlicense 16 is found in the license store 38, the DRM system 32 may thenperform the license acquisition function described below to obtain sucha valid license 16.

Assuming that one or more valid licenses 16 are found, for each validlicense 16, the license evaluator 36 of the DRM system 32 nextdetermines whether such valid license 16 gives the user the right torender the corresponding digital content 12 in the manner desired (i.e.,is enabling) (steps 607 and 609). In particular, the license evaluator36 determines whether the requesting user has the right to play therequested digital content 12 based on the rights description in eachlicense 16 and based on what the user is attempting to do with thedigital content 12. For example, such rights description may allow theuser to render the digital content 12 into a sound, but not into adecrypted digital copy.

As should be understood, the rights description in each license 16specifies whether the user has rights to play the digital content 12based on any of several factors, including who the user is, where theuser is located, what type of computing device 14 the user is using,what rendering application 34 is calling the DRM system 32, the date,the time, etc. In addition, the rights description may limit the license16 to a pre-determined number of plays, or pre-determined play time, forexample. In such case, the DRM system 32 must refer to any stateinformation with regard to the license 16, (i.e., how many times thedigital content 12 has been rendered, the total amount of time thedigital content 12 has been rendered, etc.), where such stateinformation is stored in the state store 40 of the DRM system 32 on theusers computing device 14.

Accordingly, the license evaluator 36 of the DRM system 32 reviews therights description of each valid license 16 to determine whether suchvalid license 16 confers the rights sought to the user. In doing so, thelicense evaluator 36 may have to refer to other data local to the userscomputing device 14 to perform a determination of whether the user hasthe rights sought. As seen in FIG. 4, such data may include anidentification 42 of the users computing device (machine) 14 andparticular aspects thereof, an identification 44 of the user andparticular aspects thereof, an identification of the renderingapplication 34 and particular aspects thereof, a system clock 46, andthe like. If no valid license 16 is found that provides the user withthe right to render the digital content 12 in the manner sought, the DRMsystem 32 may then perform the license acquisition function describedbelow to obtain such a license 16, if in fact such a license 16 isobtainable.

Of course, in some instances the user cannot obtain the right to renderthe digital content 12 in the manner requested, because the contentowner of such digital content 12 has in effect directed that such rightnot be granted. For example, the content owner of such digital content12 may have directed that no license 16 be granted to allow a user toprint a text document, or to copy a multimedia presentation into anun-encrypted form. In one embodiment of the present invention, thedigital content 12 includes data on what rights are available uponpurchase of a license 16, and types of licenses 16 available. However,it will be recognized that the content owner of a piece of digitalcontent 12 may at any time change the rights currently available forsuch digital content 12 by changing the licenses 16 available for suchdigital content 12.

DRM System 32—License Acquisition

Referring now to FIG. 7, if in fact the license evaluator 36 does notfind in the license store 38 any valid, enabling license 16corresponding to the requested digital content 12, the DRM system 32 maythen perform the function of license acquisition. As shown in FIG. 3,each piece of digital content 12 is packaged with information in anun-encrypted form regarding how to obtain a license 16 for renderingsuch digital content 12 (i.e., license acquisition information).

In one embodiment of the present invention, such license acquisitioninformation may include (among other things) types of licenses 16available, and one or more Internet web sites or other site informationat which one or more appropriate license servers 24 may be accessed,where each such license server 24 is in fact capable of issuing alicense 16 corresponding to the digital content 12. Of course, thelicense 16 may be obtained in other manners without departing from thespirit and scope of the present invention. For example, the license 16may be obtained from a license server 24 at an electronic bulletinboard, or even in person or via regular mail in the form of a file on amagnetic or optical disk or the like.

Assuming that the location for obtaining a license 16 is in fact alicense server 24 on a network, the license evaluator 36 thenestablishes a network connection to such license server 24 based on theweb site or other site information, and then sends a request for alicense 16 from such connected license server 24 (steps 701, 703). Inparticular, once the DRM system 32 has contacted the license server 24,such DRM system 32 transmits appropriate license request information 36to such license server 24. In one embodiment of the present invention,such license 16 request information 36 may include:

-   -   the public key of the black box 30 of the DRM system 32 (PU-BB);    -   the version number of the black box 30 of the DRM system 32;    -   a certificate with a digital signature from a certifying        authority certifying the black box 30 (where the certificate may        in fact include the aforementioned public key and version number        of the black box 30);    -   the content ID (or package ID) that identifies the digital        content 12 (or package 12 p);    -   the key ID that identifies the decryption key (KD) for        decrypting the digital content 12;    -   the type of license 16 requested (if in fact multiple types are        available);    -   the type of rendering application 34 that requested rendering of        the digital content 12;

and/or the like, among other things. Of course, greater or lessoramounts of license 16 request information 36 may be transmitted to thelicense server 24 by the DRM system 32 without departing from the spiritand scope of the present invention. For example, information on the typeof rendering application 34 may not be necessary, while additionalinformation about the user and/or the users computing device 14 may benecessary.

Once the license server 24 has received the license 16 requestinformation 36 from the DRM system 32, the license server 24 may thenperform several checks for trust/authentication and for other purposes.In one embodiment of the present invention, such license server 24checks the certificate with the digital signature of the certifyingauthority to determine whether such has been adulterated or otherwisemodified (steps 705, 707). If so, the license server 24 refuses to grantany license 16 based on the request information 36. The license server24 may also maintain a list of known ‘bad’ users and/or users computingdevices 14, and may refuse to grant any license 16 based on a requestfrom any such bad user and/or bad users computing device 14 on the list.Such ‘bad’ list may be compiled in any appropriate manner withoutdeparting from the spirit and scope of the present invention.

Based on the received request and the information associated therewith,and particularly based on the content ID (or package ID) in the licenserequest information, the license server 24 can interrogate thecontent-key database 20 (FIG. 1) and locate a record corresponding tothe digital content 12 (or package 12 p) that is the basis of therequest. As was discussed above, such record contains the decryption key(KD), key ID, and content ID for such digital content 12. In addition,such record may contain license data regarding the types of licenses 16to be issued for the digital content 12 and the terms and conditions foreach type of license 16. Alternatively, such record may include apointer, link, or reference to a location having such additionalinformation.

As mentioned above, multiple types of licenses 16 may be available. Forexample, for a relatively small license fee, a license 16 allowing alimited number of renderings may be available. For a relatively greaterlicense fee, a license 16 allowing unlimited renderings until anexpiration date may be available. For a still greater license fee, alicense 16 allowing unlimited renderings without any expiration date maybe available. Practically any type of license 16 having any kind oflicense terms may be devised and issued by the license server 24 withoutdeparting from the spirit and scope of the present invention.

In one embodiment of the present invention, the request for a license 16is accomplished with the aid of a web page or the like as transmittedfrom the license server 24 to the user's computing device 14.Preferably, such web page includes information on all types of licenses16 available from the license server 24 for the digital content 12 thatis the basis of the license 16 request.

In one embodiment of the present invention, prior to issuing a license16, the license server 24 checks the version number of the black box 30to determine whether such black box 30 is relatively current (steps 709,711). As should be understood, the black box 30 is intended to be secureand protected from attacks from a user with nefarious purposes (i.e., toimproperly render digital content 12 without a license 16, or outsidethe terms of a corresponding license 16). However, it is to berecognized that no system and no software device is in fact totallysecure from such an attack.

As should also be understood, if the black box 30 is relatively current,i.e., has been obtained or updated relatively recently, it is lesslikely that such black box 30 has been successfully attacked by such anefarious user. Preferably, and as a matter of trust, if the licenseserver 24 receives a license request with request information 36including a black box 30 version number that is not relatively current,such license server 24 refuses to issue the requested license 16 untilthe corresponding black box 30 is upgraded to a current version, as willbe described below. Put simply, the license server 24 will not trustsuch black box 30 unless such black box 30 is relatively current.

In the context of the black box 30 of the present invention, the term‘current’ or ‘relatively current’ may have any appropriate meaningwithout departing from the spirit and scope of the present invention,consistent with the function of providing trust in the black box 30based on the age or use thereof. For example, ‘current’ may be definedaccording to age (i.e., less than one month old). As an alternativeexample, ‘current’ may be defined based on a number of times that theblack box 30 has decrypted digital content 12 (i.e., less than 200instances of decryption). Moreover, ‘current’ may be based on policy asset by each license server 24, where one license server 24 may define‘current’ differently from another license server 24, and a licenseserver 24 may further define ‘current’ differently depending on thedigital content 12 for which a license 16 is requested, or depending onthe type of license 16 requested, among other things.

Assuming that the license server 24 is satisfied from the version numberof a black box 30 or other indicia thereof that such black box 30 iscurrent, the license server 24 then proceeds to negotiate terms andconditions for the license 16 with the user (step 713). Alternatively,the license server 24 negotiates the license 16 with the user, thensatisfies itself from the version number of the black box 30 that suchblack box 30 is current (i.e., performs step 713, then step 711). Ofcourse, the amount of negotiation varies depending on the type oflicense 16 to be issued, and other factors. For example, if the licenseserver 24 is merely issuing a paid-up unlimited use license 16, verylittle need be negotiated. On the other hand, if the license 16 is to bebased on such items as varying values, sliding scales, break points, andother details, such items and details may need to be worked out betweenthe license server 24 and the user before the license 16 can be issued.

As should be understood, depending on the circumstances, the licensenegotiation may require that the user provide further information to thelicense server 24 (for example, information on the user, the userscomputing device 14, etc.). Importantly, the license negotiation mayalso require that the user and the license server 24 determine amutually acceptable payment instrument (a credit account, a debitaccount, a mailed check, etc.) and/or payment method (paid-upimmediately, spread over a period of time, etc.), among other things.

Once all the terms of the license 16 have been negotiated and agreed toby both the license server 24 and user (step 715), a digital license 16is generated by the license server 24 (step 719), where such generatedlicense 16 is based at least in part on the license request the blackbox 30 public key (PU-BB), and the decryption key (KD) for the digitalcontent 12 that is the basis of the request as obtained from thecontent-key database 20. In one embodiment of the present invention, andas seen in FIG. 8, the generated license 16 includes:

-   -   the content ID of the digital content 12 to which the license 16        applies;    -   a Digital Rights License (DRL) 48 (i.e., the rights description        or actual terms and conditions of the license 16 written in a        predetermined form that the license evaluator 36 can        interrogate), perhaps encrypted with the decryption key (KD)        (i.e., KD (DRL));    -   the decryption key (KD) for the digital content 12 encrypted        with the black box 30 public key (PU-BB) as receive in the        license request (i.e., (PU-BB (KD));    -   a digital signature from the license server 24 (without any        attached certificate) based on (KD (DRL)) and (PU-BB (KD)) and        encrypted with the license server 24 private key (i.e., (S        (PR-LS))); and    -   the certificate that the license server 24 obtained previously        from the content server 22, such certificate indicating that the        license server 24 has the authority from the content server 22        to issue the license 16 (i.e., (CERT (PU-LS) S (PR-CS))).

As should be understood, the aforementioned elements and perhaps othersare packaged into a digital file or some other appropriate form. Asshould also be understood, if the DRL 48 or (PU-BB (KD)) in the license16 should become adulterated or otherwise modified, the digitalsignature (S (PR-LS)) in the license 16 will not match and thereforewill not validate such license 16. For this reason, the DRL 48 need notnecessarily be in an encrypted form (i.e., (KD(DRL)) as mentionedabove), although such encrypted form may in some instances be desirableand therefore may be employed without departing from the spirit andscope of the present invention.

Once the digital license 16 has been prepared, such license 16 is thenissued to the requester (i.e., the DRM system 32 on the user's computingdevice 14) (step 719 of FIG. 7). Preferably, the license 16 istransmitted over the same path through which the request therefor wasmade (i.e., the Internet or another network), although another path maybe employed without departing from the spirit and scope of the presentinvention. Upon receipt, the requesting DRM system 32 preferablyautomatically places the received digital license 16 in the licensestore 38 (step 721).

It is to be understood that a users computing device 14 may on occasionmalfunction, and licenses 16 stored in the license store 38 of the DRMsystem 32 on such users computing device 14 may become irretrievablylost. Accordingly, it is preferable that the license server 24 maintaina database 50 of issued licenses 16 (FIG. 1), and that such licenseserver 24 provide a user with a copy or re-issue (hereinafter‘re-issue’) of an issued license 16 if the user is in fact entitled tosuch re-issue. In the aforementioned case where licenses 16 areirretrievably lost, it is also likely the case that state informationstored in the state store 40 and corresponding to such licenses 16 isalso lost. Such lost state information should be taken into account whenre-issuing a license 16. For example, a fixed number of renderingslicense 16 might legitimately be re-issued in a pro-rated form after arelatively short period of time, and not re-issued at all after arelatively longer period of time.

DRM System 32—Installation/Upgrade of Black Box 30

As was discussed above, as part of the function of acquiring a license16, the license server 24 may deny a request for a license 16 from auser if the users computing device 14 has a DRM system 32 with a blackbox 30 that is not relatively current, i.e., has a relatively oldversion number. In such case, it is preferable that the black box 30 ofsuch DRM system 32 be upgraded so that the license acquisition functioncan then proceed. Of course, the black box 30 may be upgraded at othertimes without departing from the spirit and scope of the presentinvention.

Preferably, as part of the process of installing the DRM system 32 on ausers computing device 14, a non-unique ‘lite’ version of a black box 30is provided. Such ‘lite’ black box 30 is then upgraded to a uniqueregular version prior to rendering a piece of digital content 12. Asshould be understood, if each black box 30 in each DRM system 32 isunique, a security breach into one black box 30 cannot easily bereplicated with any other black box 30.

Referring now to FIG. 9, the DRM system 32 obtains the unique black box30 by requesting same from a black box server 26 or the like (as wasdiscussed above and as shown in FIG. 1) (step 901). Typically, suchrequest is made by way of the Internet, although other means of accessmay be employed without departing from the spirit and scope of thepresent invention. For example, the connection to a black box server 26may be a direct connection, either locally or remotely. An upgrade fromone unique non-lite black box 30 to another unique non-lite black box 30may also be requested by the DRM system 32 at any time, such as forexample a time when a license server 24 deems the black box 30 notcurrent, as was discussed above.

Thereafter, the black box server 26 generates a new unique black box 30(step 903). As seen in FIG. 3, each new black box 30 is provided with aversion number and a certificate with a digital signature from acertifying authority. As was discussed above in connection with thelicense acquisition function, the version number of the black box 30indicates the relative age and/or use thereof. The certificate with thedigital signature from the certifying authority, also discussed above inconnection with the license acquisition function, is a proffer orvouching mechanism from the certifying authority that a license server24 should trust the black box 30. Of course, the license server 24 musttrust the certifying authority to issue such a certificate for a blackbox 30 that is in fact trustworthy. It may be the case, in fact, thatthe license server 24 does not trust a particular certifying authority,and refuses to honor any certificate issued by such certifyingauthority. Trust may not occur, for example, if a particular certifyingauthority is found to be engaging in a pattern of improperly issuingcertificates.

Preferably, and as was discussed above, the black box server 26 includesa new unique public/private key pair (PU-BB, PR-BB) with the newlygenerated unique black box 30 (step 903 of FIG. 9). Preferably, theprivate key for the black box 30 (PR-BB) is accessible only to suchblack box 30, and is hidden from and inaccessible by the remainder ofthe world, including the computing device 14 having the DRM system 32with such black box 30, and the user thereof.

Most any hiding scheme may be employed without departing from the spiritand scope of the present invention, so long as such hiding scheme infact performs the function of hiding the private key (PR-BB) from theworld. As but one example, the private key (PR-BB) may be split intoseveral sub-components, and each sub-component may be encrypted uniquelyand stored in a different location. In such a situation, it ispreferable that such sub-components are never assembled in full toproduce the entire private key (PR-BB).

In one embodiment of the present invention, such private key (PR-BB) isencrypted according to code-based encryption techniques. In particular,in such embodiment, the actual software code of the black box 30 (orother software code) is employed as encrypting key(s). Accordingly, ifthe code of the black box 30 (or the other software code) becomesadulterated or otherwise modified, for example by a user with nefariouspurposes, such private key (PR-BB) cannot be decrypted.

Although each new black box 30 is delivered with a new public/privatekey pair (PU-BB, PR-BB), such new black box 30 is also preferably givenaccess to old public/private key pairs from old black boxes 30previously delivered to the DRM system 32 on the users computing device14 (step 905). Accordingly, the upgraded black box 30 can still employthe old key pairs to access older digital content 12 and oldercorresponding licenses 16 that were generated according to such old keypairs, as will be discussed in more detail below.

Preferably, the upgraded black box 30 delivered by the black box server26 is tightly tied to or associated with the users computing device 14.Accordingly, the upgraded black box 30 cannot be operably transferredamong multiple computing devices 14 for nefarious purposes or otherwise.In one embodiment of the present invention, as part of the request forthe black box 30 (step 901) the DRM system 32 provides hardwareinformation unique to such DRM system 32 and/or unique to the userscomputing device 14 to the black box server 26, and the black box server26 generates a black box 30 for the DRM system 32 based in part on suchprovided hardware information. Such generated upgraded black box 30 isthen delivered to and installed in the DRM system 32 on the userscomputing device 14 (steps 907, 909). If the upgraded black box 30 isthen somehow transferred to another computing device 14, the transferredblack box 30 recognizes that it is not intended for such other computingdevice 14, and does not allow any requested rendering to proceed on suchother computing device 14.

Once the new black box 30 is installed in the DRM system 32, such DRMsystem 32 can proceed with a license acquisition function or with anyother function.

DRM System 32—Content Rendering, Part 3

Referring now to FIG. 5B, and assuming, now, that the license evaluator36 has found at least one valid license 16 and that at least one of suchvalid licenses 16 provides the user with the rights necessary to renderthe corresponding digital content 12 in the manner sought (i.e., isenabling), the license evaluator 36 then selects one of such licenses 16for further use (step 519). Specifically, to render the requesteddigital content 12, the license evaluator 36 and the black box 30 incombination obtain the decryption key (KD) from such license 16, and theblack box 30 employs such decryption key (KD) to decrypt the digitalcontent 12. In one embodiment of the present invention, and as wasdiscussed above, the decryption key (KD) as obtained from the license 16is encrypted with the black box 30 public key (PU-BB(KD)), and the blackbox 30 decrypts such encrypted decryption key with its private key(PR-BB) to produce the decryption key (KD) (steps 521, 523). However,other methods of obtaining the decryption key (KD) for the digitalcontent 12 may be employed without departing from the spirit and scopeof the present invention.

Once the black box 30 has the decryption key (KD) for the digitalcontent 12 and permission from the license evaluator 36 to render thedigital content 12, control may be returned to the rendering application34 (steps 525, 527). In one embodiment of the present invention, therendering application 34 then calls the DRM system 32/black box 30 anddirects at least a portion of the encrypted digital content 12 to theblack box 30 for decryption according to the decryption key (KD) (step529). The black box 30 decrypts the digital content 12 based upon thedecryption key (KD) for the digital content 12, and then the black box30 returns the decrypted digital content 12 to the rendering application34 for actual rendering (steps 533, 535). The rendering application 34may either send a portion of the encrypted digital content 12 or theentire digital content 12 to the black box 30 for decryption based onthe decryption key (KD) for such digital content 12 without departingfrom the spirit and scope of the present invention.

Preferably, when the rendering application 34 sends digital content 12to the black box 30 for decryption, the black box 30 and/or the DRMsystem 32 authenticates such rendering application 34 to ensure that itis in fact the same rendering application 34 that initially requestedthe DRM system 32 to run (step 531). Otherwise, the potential existsthat rendering approval may be obtained improperly by basing therendering request on one type of rendering application 34 and in factrendering with another type of rendering application 34. Assuming theauthentication is successful and the digital content 12 is decrypted bythe black box 30, the rendering application 34 may then render thedecrypted digital content 12 (steps 533, 535).

Sequence of Key Transactions

Referring now to FIG. 10, in one embodiment of the present invention, asequence of key transactions is performed to obtain the decryption key(KD) and evaluate a license 16 for a requested piece of digital content12 (i.e., to perform steps 515-523 of FIGS. 5A and 5B). Mainly, in suchsequence, the DRM system 32 obtains the decryption key (KD) from thelicense 16, uses information obtained from the license 16 and thedigital content 12 to authenticate or ensure the validity of both, andthen determines whether the license 16 in fact provides the right torender the digital content 12 in the manner sought. If so, the digitalcontent 12 may be rendered.

Bearing in mind that each license 16 for the digital content 12, as seenin FIG. 8, includes:

-   -   the content ID of the digital content 12 to which the license 16        applies;    -   the Digital Rights License (DRL) 48, perhaps encrypted with the        decryption key (KD) (i.e., KD (DRL));    -   the decryption key (KD) for the digital content 12 encrypted        with the black box 30 public key (PU-BB) (i.e., (PU-BB (KD));    -   the digital signature from the license server 24 based on (KD        (DRL)) and (PU-BB (KD)) and encrypted with the license server 24        private key (i.e., (S (PR-LS))); and    -   the certificate that the license server 24 obtained previously        from the content server 22 (i.e., (CERT (PU-LS) S (PR-CS))),

and also bearing in mind that the package 12 p having the digitalcontent 12, as seen in FIG. 3, includes:

-   -   the content ID of such digital content 12;    -   the digital content 12 encrypted by KD (i.e., (KD(CONTENT)));    -   a license acquisition script that is not encrypted; and    -   the key KD encrypting the content server 22 public key (PU-CS),        signed by the content server 22 private key (PR-CS) (i.e., (KD        (PU-CS) S (PR-CS))),

in one embodiment of the present invention, the specific sequence of keytransactions that are performed with regard to a specific one of thelicenses 16 for the digital content 12 is as follows:

1. Based on (PU-BB (KD)) from the license 16, the black box 30 of theDRM system 32 on the users computing device 14 applies its private key(PR-BB) to obtain (KD) (step 1001). (PR-BB (PU-BB (KD))=(KD)). Note,importantly, that the black box 30 could then proceed to employ KD todecrypt the digital content 12 without any further ado. However, andalso importantly, the license server 24 trusts the black box 30 not todo so. Such trust was established at the time such license server 24issued the license 16 based on the certificate from the certifyingauthority vouching for the trustworthiness of such black box 30.Accordingly, despite the black box 30 obtaining the decryption key (KD)as an initial step rather than a final step, the DRM system 32 continuesto perform all license 16 validation and evaluation functions, asdescribed below.

2. Based on (KD (PU-CS) S (PR-CS)) from the digital content 12, theblack box 30 applies the newly obtained decryption key (KD) to obtain(PU-CS) (step 1003). (KD (KD (PU-CS))=(PU-CS)). Additionally, the blackbox 30 can apply (PU-CS) as against the signature (S (PR-CS)) to satisfyitself that such signature and such digital content 12/package 12 p isvalid (step 1005). If not valid, the process is halted and access to thedigital content 12 is denied.

3. Based on (CERT (PU-LS) S (PR-CS)) from the license 16, the black box30 applies the newly obtained content server 22 public key (PU-CS) tosatisfy itself that the certificate is valid (step 1007), signifyingthat the license server 24 that issued the license 16 had the authorityfrom the content server 22 to do so, and then examines the certificatecontents to obtain (PU-LS) (step 1009). If not valid, the process ishalted and access to the digital content 12 based on the license 16 isdenied.

4. Based on (S (PR-LS)) from the license 16, the black box 30 appliesthe newly obtained license server 24 public key (PU-LS) to satisfyitself that the license 16 is valid (step 1011). If not valid, theprocess is halted and access to the digital content 12 based on thelicense 16 is denied.

5. Assuming all validation steps are successful, and that the DRL 48 inthe license 16 is in fact encrypted with the decryption key (KD), thelicense evaluator 36 then applies the already-obtained decryption key(KD) to (KD(DRL)) as obtained from the license 16 to obtain the licenseterms from the license 16 (i.e., the DRL 48) (step 1013). Of course, ifthe DRL 48 in the license 16 is not in fact encrypted with thedecryption key (KD), step 1013 may be omitted. The license evaluator 36then evaluates/interrogates the DRL 48 and determines whether the userscomputing device 14 has the right based on the DRL 48 in the license 16to render the corresponding digital content 12 in the manner sought(i.e., whether the DRL 48 is enabling) (step 1015). If the licenseevaluator 36 determines that such right does not exist, the process ishalted and access to the digital content 12 based on the license 16 isdenied.

6. Finally, assuming evaluation of the license 16 results in a positivedetermination that the users computing device 14 has the right based onthe DRL 48 terms to render the corresponding digital content 12 in themanner sought, the license evaluator 36 informs the black box 30 thatsuch black box 30 can render the corresponding digital content 12according to the decryption key (KD). The black box 30 thereafterapplies the decryption key (KD) to decrypt the digital content 12 fromthe package 12 p (i.e., (KD(KD(CONTENT))=(CONTENT)) (step 1017).

It is important to note that the above-specified series of stepsrepresents an alternating or ‘ping-ponging’ between the license 16 andthe digital content 12. Such ping-ponging ensures that the digitalcontent 12 is tightly bound to the license 16, in that the validationand evaluation process can only occur if both the digital content 12 andlicense 16 are present in a properly issued and valid form. In addition,since the same decryption key (KD) is needed to get the content server22 public key (PU-CS) from the license 16 and the digital content 12from the package 12 p in a decrypted form (and perhaps the license terms(DRL 48) from the license 16 in a decrypted form), such items are alsotightly bound. Signature validation also ensures that the digitalcontent 12 and the license 16 are in the same form as issued from thecontent server 22 and the license server 24, respectively. Accordingly,it is difficult if not impossible to decrypt the digital content 12 bybypassing the license server 24, and also difficult if not impossible toalter and then decrypt the digital content 12 or the license 16.

In one embodiment of the present invention, signature verification, andespecially signature verification of the license 16, is alternatelyperformed as follows. Rather than having a signature encrypted by theprivate key of the license server 16 (PR-LS), as is seen in FIG. 8, eachlicense 16 has a signature encrypted by a private root key (PR-R) (notshown), where the black box 30 of each DRM system 32 includes a publicroot key (PU-R) (also not shown) corresponding to the private root key(PR-R). The private root key (PR-R) is known only to a root entity, anda license server 24 can only issue licenses 16 if such license server 24has arranged with the root entity to issue licenses 16.

In particular, in such embodiment:

1. the license server 24 provides its public key (PU-LS) to the rootentity;

2. the root entity returns the license server public key (PU-LS) to suchlicense server 24 encrypted with the private root key (PR-R) (i.e.,(CERT (PU-LS) S (PR-R))); and

3. the license server 24 then issues a license 16 with a signatureencrypted with the license server private key (S (PR-LS)), and alsoattaches to the license the certificate from the root entity (CERT(PU-LS) S (PR-R)).

For a DRM system 18 to validate such issued license 16, then, the DRMsystem 18:

1. applies the public root key (PU-R) to the attached certificate (CERT(PU-LS) S (PR-R)) to obtain the license server public key (PU-LS); and

2. applies the obtained license server public key (PU-LS) to thesignature of the license 16 (S (PR-LS).

Importantly, it should be recognized that just as the root entity gavethe license server 24 permission to issue licenses 16 by providing thecertificate (CERT (PU-LS) S (PR-R)) to such license server 24, suchlicense server 24 can provide a similar certificate to a second licenseserver 24 (i.e., (CERT (PU-LS2) S (PR-LS1)), thereby allowing the secondlicense server to also issue licenses 16. As should now be evident, alicense 16 issued by the second license server would include a firstcertificate (CERT (PU-LS1) S (PR-R)) and a second certificate (CERT(PU-LS2) S (PR-LS1)). Likewise, such license 16 is validated byfollowing the chain through the first and second certificates. Ofcourse, additional links in the chain may be added and traversed.

One advantage of the aforementioned signature verification process isthat the root entity may periodically change the private root key(PR-R), thereby likewise periodically requiring each license server 24to obtain a new certificate (CERT (PU-LS) S (PR-R)). Importantly, as arequirement for obtaining such new certificate, each license server maybe required to upgrade itself. As with the black box 30, if a licenseserver 24 is relatively current, i.e., has been upgraded relativelyrecently, it is less likely that license server 24 has been successfullyattacked. Accordingly, as a matter of trust, each license server 24 ispreferably required to be upgraded periodically via an appropriateupgrade trigger mechanism such as the signature verification process. Ofcourse, other upgrade mechanisms may be employed without departing fromthe spirit and scope of the present invention.

Of course, if the private root key (PR-R) is changed, then the publicroot key (PU-R) in each DRM system 18 must also be changed. Such changemay for example take place during a normal black box 30 upgrade, or infact may require that a black box 30 upgrade take place. Although achanged public root key (PU-R) may potentially interfere with signaturevalidation for an older license 16 issued based on an older private rootkey (PR-R), such interference may be minimized by requiring that anupgraded black box 30 remember all old public root keys (PU-R).Alternatively, such interference may be minimized by requiring signatureverification for a license 16 only once, for example the first time suchlicense 16 is evaluated by the license evaluator 36 of a DRM system 18.In such case, state information on whether signature verification hastaken place should be compiled, and such state information should bestored in the state store 40 of the DRM system 18.

Digital Rights License 48

In the present invention, the license evaluator 36 evaluates a DigitalRights License (DRL) 48 as the rights description or terms of a license16 to determine if such DRL 48 allows rendering of a corresponding pieceof digital content 12 in the manner sought. In one embodiment of thepresent invention, the DRL 48 may be written by a licensor (i.e., thecontent owner) in any DRL language.

As should be understood, there are a multitude of ways to specify a DRL48. Accordingly, a high degree of flexibility must be allowed for in anyDRL language. However, it is impractical to specify all aspects of a DRL48 in a particular license language, and it is highly unlikely that theauthor of such a language can appreciate all possible licensing aspectsthat a particular digital licensor may desire. Moreover, a highlysophisticated license language may be unnecessary and even a hindrancefor a licensor providing a relatively simple DRL 48. Nevertheless, alicensor should not be unnecessarily restricted in how to specify a DRL48. At the same time, the license evaluator 36 should always be able toget answers from a DRL 48 regarding a number of specific licensequestions.

In the present invention, and referring now to FIG. 11, a DRL 48 can bespecified in any license language, but includes a language identifier ortag 54. The license evaluator 36 evaluating the license 16, then,performs the preliminary step of reviewing the language tag 54 toidentify such language, and then selects an appropriate license languageengine 52 for accessing the license 16 in such identified language. Asshould be understood, such license language engine 52 must be presentand accessible to the license evaluator 36. If not present, the languagetag 54 and/or the DRL 48 preferably includes a location 56 (typically aweb site) for obtaining such language engine 52.

Typically, the language engine 52 is in the form of an executable fileor set of files that reside in a memory of the user's computing device14, such as a hard drive. The language engine 52 assists the licenseevaluator 36 to directly interrogate the DRL 48, the license evaluator36 interrogates the DRL 48 indirectly via the language engine 48 actingas an intermediary, or the like. When executed, the language engine 52runs in a work space in a memory of the users computing device 14, suchas RAM. However, any other form of language engine 52 may be employedwithout departing from the spirit and scope of the present invention.

Preferably, any language engine 52 and any DRL language supports atleast a number of specific license questions that the license evaluator36 expects to be answered by any DRL 48, as will be discussed below.Accordingly, the license evaluator 36 is not tied to any particular DRLlanguage; a DRL 48 may be written in any appropriate DRL language; and aDRL 48 specified in a new license language can be employed by anexisting license evaluator 36 by having such license evaluator 36 obtaina corresponding new language engine 52.

DRL Languages

Two examples of DRL languages, as embodied in respective DRLs 48, areprovided below. The first, ‘simple’ DRL 48 is written in a DRL languagethat specifies license attributes, while the second ‘script’ DRL 48 iswritten in a DRL language that can perform functions according to thescript specified in the DRL 48. While written in a DRL language, themeaning of each line of code should be apparent based on the linguisticsthereof and/or on the attribute description chart that follows:

Simple DRL 48: <LICENSE> <DATA> <NAME>Beastie Boy's Play</NAME><ID>39384</ID> <DESCRIPTlON>Play the song 3 times</DESCRIPTION><TERMS></TERMS> <VALIDITY> <NOTBEFORE>19980102 23:20:14Z</NOTBEFORE><NOTAFTER>19980102 23:20:14Z</NOTAFTER> </VALIDITY> <ISSUEDDATE>1998010223:20:14Z</ISSUEDDATE> <LICENSORSITE>http://www.foo.com</LICENSORSITE><CONTENT> <NAME>Beastie Boy's</NAME> <ID>392</ID> <KEYID>39292</KEYID><TYPE>MS Encrypted ASF 2.0</TTYPE> </CONTENT> <OWNER><ID>939KDKD393KD</ID> <NAME>Universal</NAME> <PUBLICKEY></PUBLICKEY></OWNER> <LICENSEE> <NAME>Arnold</NAME> <ID>939KDKD393KD</ID><PUBLICKEY></PUBLICKEY> </LICENSEE> <PRINCIPAL TYPE==AND=> <PRINCIPALTYPE==OR=> <PRINCIPAL> <TYPE>x86Computer</TYPE><ID>3939292939d9e939</ID> <NAME>Personal Computer</NAME> <AUTHTYPE>IntelAuthenticated Boot PC SHA-1 DSA512</AUTHTYPE><AUTHDATA>29293939</AUTHDATA> </PRINCIPAL> <PRINCIPAL><TYPE>Application</TYPE> <ID>2939495939292</ID> <NAME>Window=s MediaPlayer</NAME> <AUTHTYPE>Authenticode SHA-1</AUTHTYPE><AUTHDATA>93939</AUTHDATA> </PRINCIPAL> </PRINCIPAL> <PRINCIPAL><TYPE>Person</TYPE> <ID>39299482010</ID> <NAME>Arnold Blinn</NAME><AUTHTYPE>Authenticate user</AUTHTYPE><AUTHDATA>\\redmond\arnoldb</AUTHDATA> </PRINCIPAL> </PRINCIPAL><DRLTYPE>Simple</DRLTYPE>[the language tag 54] <DRLDATA> <START>1998010223:20:14Z</START> <END>19980102 23:20:14Z</END> <COUNT>3</COUNT><ACTION>PLAY</ACTION> </DRLDATA><ENABLINGBITS>aaaabbbbccccdddd</ENABLINGBITS> </DATA> <SIGNATURE><SIGNERNAME>Universal</SIGNERNAME> <SIGNERID>9382ABK3939DKD</SIGNERID><HASHALGORITHMID>MD5</HASHALGORITHMID> <SIGNALGORITHMID>RSA128</SIGNALGORITHMID> <SIGNATURE>xxxyyyxxxyyyxxxyyy</SIGNATURE><SIGNERPUBLICKEY></SIGNERPUBLICKEY><CONTENTSIGNEDSIGNERPUBLICKEY></CONTENTSIGNEDSIGNERPUBLICKEY></SIGNATURE> </LICENSE> Script DRL 48: <LICENSE> <DATA> <NAME>BeastieBoy's Play</NAME> <ID>39384</ID> <DESCRIPTION>Play the songunlimited</DESCRIPTION> <TERMS></TERMS> <VALIDITY> <NOTBEFORE>1998010223:20:14Z</NOTBEFORE> <NOTAFTER>19980102 23:20:14Z</NOTAFTER></VALIDITY> <ISSUEDDATE>19980102 23:20:14Z</ISSUEDDATE><LICENSORSITE>http://www.foo.com</LICENSORSITE> <CONTENT> <NAME>BeastieBoy's</NAME <ID>392</ID> <KEYID>39292</KEYID> <TYPE>MS Encrypted ASF2.0</TTYPE> </CONTENT> <OWNER> <ID>939KDKD393KD</ID><NAME>Universal</NAME> <PUBLICKEY></PUBLICKEY> </OWNER> <LICENSEE><NAME>Arnold</NAME> <ID>939KDKD393KD</ID> <PUBLICKEY></PUBLICKEY></LICENSEE> <DRLTYPE>Script</DRLTYPE>[the language tag 54] <DRLDATA>function on_enable(action, args) as boolean result = False if action =“PLAY” then result = True end if on_action = False end function . . .</DRLDATA> </DATA> <SIGNATURE> <SIGNERNAME>Universal</SIGNERNAME><SIGNERID>9382</SIGNERID> <SIGNERPUBLICKEY></SIGNERPUBLICKEY><HASHID>MD5</HASHID> <SIGNID>RSA 128</SIGNID><SIGNATURE>xxxyyyxxxyyyxxxyyy</SIGNATURE><CONTENTSIGNEDSIGNERPUBLICKEY></CONTENTSIGNEDSIGNERPUBLICKEY></SIGNATURE> </LICENSE>

In the two DRLs 48 specified above, the attributes listed have thefollowing descriptions and data types:

Attribute Description Data Type Id ID of the license GUID Name Name ofthe license String Content Id ID of the content GUID Content Key Id IDfor the encryption key GUID of the content Content Name Name of thecontent String Content Type Type of the content String Owner Id ID ofthe owner of the GUID content Owner Name Name of the owner of the Stringcontent Owner Public Key Public key for owner of String content. This isa base- 64 encoded public key for the owner of the content. Licensee IdId of the person getting GUID license. It may be null. Licensee NameName of the person String getting license. It may be null. LicenseePublic Key Public key of the String licensee. This is the base-64encoded public key of the licensee. It may be null. Description Simplehuman readable String description of the license Terms Legal terms ofthe String license. This may be a pointer to a web page containing legalprose. Validity Not After Validity period of license Date expirationValidity Not Before Validity period of license Date start Issued DateDate the license was Date issued DRL Type Type of the DRL. StringExample include ASIMPLE@ or ASCRIPT@ DRL Data Data specific to the DRLString Enabling Bits These are the bits that String enable access to theactual content. The interpretation of these bits is up to theapplication, but typically this will be the private key for decryptionof the content. This data will be base-64 encoded. Note that these bitsare encrypted using the public key of the individual machine. Signer IdID of person signing GUID license Signer Name Name of person signingString license Signer Public Key Public key for person String signinglicense. This is the base-64 encode public key for the signer. ContentSigned Signer Public key for person String Public Key signing thelicense that has been signed by the content server private key. Thepublic key to verify this signature will be encrypted in the content.This is base-64 encoded. Hash Alg Id Algorithm used to String generatehash. This is a string, such as AMD5@. Signature Alg Id Algorithm usedto String generate signature. This is a string, such as ARSA 128@.Signature Signature of the data. String This is base-64 encoded data.Methods

As was discussed above, it is preferable that any language engine 52 andany DRL language support at least a number of specific license questionsthat the digital license evaluator 36 expects to be answered by any DRL48. Recognizing such supported questions may include any questionswithout departing from the spirit and scope of the present invention,and consistent with the terminology employed in the two DRL 48 examplesabove, in one embodiment of the present invention, such supportedquestions or ‘methods’ include ‘access methods’, ‘DRL methods’, and‘enabling use methods’, as follows:

Access Methods

Access methods are used to query a DRL 48 for top-level attributes.

VARIANT QueryAttribute (BSTR key)

Valid keys include License.Name, License.Id, Content.Name, Content.Id,Content.Type, Owner.Name, Owner.Id, Owner.PublicKey, Licensee.Name,Licensee.Id, Licensee.PublicKey, Description, and Terms, each returninga BSTR variant; and Issued, Validity.Start and Validity.End, eachreturning a Date Variant.

DRL Methods

The implementation of the following DRL methods varies from DRL 48 toDRL 48. Many of the DRL methods contain a variant parameter labeled‘data’ which is intended for communicating more advanced informationwith a DRL 48. It is present largely for future expandability.

Boolean IsActivated(Variant data)

This method returns a Boolean indicating whether the DRL 48/license 16is activated. An example of an activated license 16 is a limitedoperation license 16 that upon first play is active for only 48 hours.

Activate(Variant data)

This method is used to activate a license 16. Once a license 16 isactivated, it cannot be deactivated.

Variant QueryDRL(Variant data)

This method is used to communicate with a more advanced DRL 48. It islargely about future expandability of the DRL 48 feature set.

Variant GetExpires(BSTR action, Variant data)

This method returns the expiration date of a license 16 with regard tothe passed-in action. If the return value is NULL, the license 16 isassumed to never expire or does not yet have an expiration date becauseit hasn't been activated, or the like.

Variant GetCount(BSTR action, Variant data)

This method returns the number of operations of the passed-in actionthat are left. If NULL is returned, the operation can be performed anunlimited number of times.

Boolean IsEnabled(BSTR action, Variant data)

This method indicates whether the license 16 supports the requestedaction at the present time.

Boolean IsSunk(BSTR action, Variant data)

This method indicates whether the license 16 has been paid for. Alicense 16 that is paid for up front would return TRUE, while a license16 that is not paid for up front, such as a license 16 that collectspayments as it is used, would return FALSE.

Enabling Use Methods.

These methods are employed to enable a license 16 for use in decryptingcontent.

Boolean Validate (BSTR key)

This method is used to validate a license 16. The passed-in key is theblack box 30 public key (PU-BB) encrypted by the decryption key (KD) forthe corresponding digital content 12 (i.e., (KD(PU-BB))) for use invalidation of the signature of the license 16. A return value of TRUEindicates that the license 16 is valid. A return value of FALSEindicates invalid.

int OpenLicense 16(BSTR action, BSTR key, Variant data)

This method is used to get ready to access the decrypted enabling bits.The passed-in key is (KD(PU-BB)) as described above. A return value of 0indicates success. Other return values can be defined.

BSTR GetDecryptedEnablingBits (BSTR action, Variant data)

Variant GetDecryptedEnablingBitsAsBinary (BSTR action, Variant Data)

These methods are used to access the enabling bits in decrypted form. Ifthis is not successful for any of a number of reasons, a null string ornull variant is returned.

void CloseLicense 16 (BSTR action, Variant data)

This method is used to unlock access to the enabling bits for performingthe passed-in action. If this is not successful for any of a number ofreasons, a null string is returned.

Heuristics

As was discussed above, if multiple licenses 16 are present for the samepiece of digital content 12, one of the licenses 16 must be chosen forfurther use. Using the above methods, the following heuristics could beimplemented to make such choice. In particular, to perform an action(say APLAY@) on a piece of digital content 12, the following steps couldbe performed:

1. Get all licenses 16 that apply to the particular piece of digitalcontent 12.

2. Eliminate each license 16 that does not enable the action by callingthe IsEnabled function on such license 16.

3. Eliminate each license 16 that is not active by calling IsActivatedon such license 16.

4. Eliminate each license 16 that is not paid for up front by callingIsSunk on such license 16.

5. If any license 16 is left, use it. Use an unlimited-number-of-playslicense 16 before using a limited-number-of-plays license 16, especiallyif the unlimited-number-of-plays license 16 has an expiration date. Atany time, the user should be allowed to select a specific license 16that has already been acquired, even if the choice is notcost-effective. Accordingly, the user can select a license 16 based oncriteria that are perhaps not apparent to the DRM system 32.

6. If there are no licenses 16 left, return status so indicating. Theuser would then be given the option of:

using a license 16 that is not paid for up front, if available;

activating a license 16, if available; and/or

performing license acquisition from a license server 24.

Rendering Digital Content on a Portable Device or the Like

Referring now to FIG. 13, it is to be appreciated that in one mode ofobtaining and rendering digital content 12, such digital content 12 isdownloaded or otherwise placed on a personal computer 60 or the like,and the corresponding digital license 16 once obtained is also isdownloaded or otherwise placed on the personal computer 60 or the like.Typically, the personal computer 60 or the like is a relatively largeand not easily movable device, and requires a power line connection forreceiving externally supplied power, and a communications lineconnection for communicating with the world. In addition, and as wasdiscussed in connection with FIG. 12, the computer 60 may include acable-connected keyboard, a cable-connected mouse, a cable-connectedscreen, and the like, and may be coupled to a scanner, a printer, and/orother peripheral devices. Thus, the computer 60 is relatively tied downor ‘tethered’ by such connections and peripherals.

Of course, the personal computer 60 of FIG. 13 becomes un-tethered by,for example, disconnecting the peripherals, and becomes more un-tetheredby embodying the computer 60 in the form of a full-function lap-topcomputer having the screen, keyboard, mouse, and a battery power supplybuilt in. Nevertheless, a user wishing to render digital content 12 suchas for example a musical selection while for example exercising wouldcertainly balk at carrying such a laptop computer 60 during suchactivity, even if such lap-top computer 60 weighs only four or fivepounds. Moreover, even if such full-function lap-top computer 60 wasmade to be light-weight, perhaps on the order of two to four ounces, thecomputer 60 still would contain sensitive components (the hard drive,e.g.) that are likely to be damaged during such activity.

Fortunately, and again referring to FIG. 13, un-tethered, light-weight,truly portable computing devices 62 exist and can be employed to storeand render at least some forms of digital content 12. For example, theDIAMOND RIO portable music player, marketed by S3 Incorporated of SantaClara, Calif. is battery-operated, fits in a palm or pocket, has nomoving parts, includes large amounts of onboard flash memory to holddigital content 12, and can render the digital content 12 if for examplein the Windows Media Audio (WMA) or the MP3 formats. Such DIAMOND RIOplayer also is supplied with an appropriate cable and has an interfacethrough which the digital content 12 may be downloaded from the computer60 by way of the cable. Other portable music players include the RCALyra, Creative Nomad II, and Pocket PC devices from Hewlett-Packard,Casio and Compaq. However, and importantly, configuring portablecomputing devices 62 to support the DRM architecture as set forth aboveraises several issues.

One issue concerns certain players that have relatively small amounts ofmemory set aside for player operations such as decrypting content,rendering content, and the like. As may be appreciated, with arelatively small amount of memory, a portable device 62 cannot performat least some DRM functions as were discussed above, such as for examplepublic-private key decryption. A solution responsive to such issue isset forth in U.S. patent application Ser. No. 09/645,887, entitled“Binding Digital Content to a Portable Storage Device Or the Like In ADigital Rights Management (DRM) System” and filed Aug. 25, 2000, herebyincorporated by reference herein in its entirety.

However, and importantly, the solution set forth in such U.S. patentapplication relies on a key system based on a global secret, and suchkey system is therefore likely globally compromised if and when theglobal secret is discovered and disseminated. Accordingly, in oneembodiment of the present invention, the portable device 62 performspublic-private key decryption by way of a portable DRM system 32 p (FIG.13) instantiated in a memory thereon. As may be appreciated, such DRMsystem 32 p and the accompanying operations such as decrypting content,rendering content, and the like are accommodated on the portable device62 by increasing the amount of memory on such portable device 62available, reducing the size of the DRM system 32 p as instantiated inthe memory, or both.

In one embodiment of the present invention, and as with the subjectmatter disclosed in the aforementioned U.S. patent application Ser. No.09/645,887, all obtaining of digital content 12 and correspondingdigital licenses 16 for the portable device 62 is performed by way of acomputer 60 or the like. In particular, the computer 60 obtains alicense 16 for corresponding digital content 16 and then issues asub-license 16 s to the portable device 62 for rendering the digitalcontent 12 on the portable device 62. Such sub-license 16 s may beissued in the course of downloading the digital content 12 from thecomputer 60 to the portable device 62, or may be issued at a time beforeor after downloading the digital content 12 from the computer 60 to theportable device 62, or at another time, all without departing from thespirit and scope of the present invention. Note that although thepresent invention is discussed in terms of a computer 60 and a portabledevice 62, as seen in FIG. 13, it will be appreciated that the presentinvention may be implemented with regard to any particular type ofcomputing device 14 other than the computer 60, as appropriate, withoutdeparting from the spirit and scope of the present invention.

Importantly, since the computer 60 performs the bulk of the licenseacquisition and content acquisition functionality for the portabledevice 62, such portable device 62 and the DRM system 32 p therein neednot include such functionality therein, except insofar as is necessaryto download the content 12 and the sub-license 16 s. Accordingly,significant license acquisition and content acquisition portions of theDRM system 32 as resident on the computer 60 may be omitted from the DRMsystem 32 p as resident on the portable device 62.

The portable device 62 may be defined as a generally closed device inthat data can be on-loaded and off-loaded only in a limited manner, useraccess to hardware within the portable device 62 is very limited, andinput and display functionality is limited to a few function keys andperhaps a small LCD screen, respectively. Thus, a content thief can dovery little in the way of examining either the memory or physicalcontents of the portable device 62 to obtain content 12 therein in anunencrypted form or decryption keys. In contrast, the computer 60 may bedefined as a generally open device in that data can be on-loaded andoff-loaded in a wide-ranging manner by any of a broad range of hardwareand/or software, user access to hardware within the portable device 62is not limited in any significant way, and input and displayfunctionality is available by way of a full-function keyboard, a mouse,a high-resolution monitor, and the like. Thus, a content thief has manypotential opportunities available to examine the memory and physicalcontents of the computer 60 to obtain content 12 therein in anunencrypted form or decryption keys. In sum, then, the portable device62 as a closed device is less susceptible to nefarious actions committedby a content thief, especially as compared to the computer 60 as an opendevice.

As a result, and also importantly, the portable device 62 and the DRMsystem 32 p therein need not include functionality therein necessary toguard against most types of content theft and decryption key theft,except insofar as is necessary during download of the content 12 and thesub-license 16 s. Accordingly, significant theft prevention portions ofthe DRM system 32 as resident on the computer 60 may be omitted from theDRM system 32 p as resident on the portable device 62.

To sum up, then, the DRM system 32 p as resident on the portable device62 need only include functionality necessary (1) to authenticate theportable device 62 to the computer 60 during downloading of asub-license 16 s to the portable device, and to facilitate suchdownloading, and (2) to render content 12 on the portable device 62according to downloaded and resident sub-license(s) 16 s, includingensuring that requirements in a sub-license 16 s are filled andobtaining the content key (KD) from the sub-license 16 s. All otherfunctionality as available in the DRM system 32 on the computer 60 iseither unnecessary in the DRM system 32 p on the portable device 62, oris inherent in the portable device 62 being a closed device.

As may be appreciated, and as was disclosed in the aforementioned U.S.patent application Ser. No. 09/645,887, the sub-license 16 s as issuedby the computer 60 specifies the limitations, if any, that must besatisfied to render the corresponding content 12 on the portable device62. Of course, the computer 60 may issue such sub-license 16 s only ifpermitted according to the terms of the corresponding license 16 asobtained by the computer 60 from an appropriate license server 24. Aswas also disclosed in the aforementioned U.S. patent application Ser.No. 09/645,887, the computer 60 re-writes at least a portion of thelicense 16 when issuing the sub-license 16 s to be in a form that ismore amenable to the portable device 62 and that ties or binds thesub-license 16 s to the portable device 62. In particular, the computer60 re-encrypts the content key (KD) for decrypting the content 12 into aform that is more amenable to decryption by the portable device 62.Here, though, the content key is re-encrypted according to the black boxpublic key of the DRM system 32 p of the portable device 62 (PU-BB-PD).

In particular, and assuming that the content key (KD) in the license 16on the computer 60 is encrypted according to an asymmetric key such asthe black box public key of the computer 60 (PU-BB-CO) in the mannerdiscussed above, the computer 60 obtains the content key (KD) byapplying the black box private key of the computer 60 (PR-BB-CO) in themanner discussed above, then re-encrypts the content key (KD) accordingto (PU-BB-PD). Thus, and as should be appreciated, the content key (KD)is obtainable by the portable device 62 at the appropriate time byapplication of the black box private key of the portable device 62(PR-BB-PD), and the sub-license 16 s is therefore tied or bound to theportable device 62. As should be appreciated, without re-encrypting thecontent key (KD), the portable device 62, which would not know(PR-BB-CO), would not be able to decrypt (PU-BB-CO (KD)) to obtain (KD).

Delivering the Content 12 and the Sub-License 16S to the Portable Device62

Referring now to FIGS. 14 and 15, then, in one embodiment of the presentinvention, digital content 12 and a corresponding sub-license 16 s aredownloaded to a portable device 62 according to the following steps.Preliminarily, the portable device 62 must be coupled to an appropriatecomputer 60 by way of an appropriate connection 64 in the manner shownin FIG. 13 (step 1401). The connection 64 may be any appropriateconnection without departing from the spirit and scope of the presentinvention. Typically, though, the portable device 62 has one or moreinterfaces 66 and such interface(s) 66 dictate the types of connections64 that may be employed. For example, the interface 66 may be a serialport, a parallel port, a USB port, a ‘fire wire’ port, an infrared port,or the like, in which case a corresponding type of connection 64 must beemployed, assuming the computer 60 supports such connection 64 by way ofa corresponding interface 68 and appropriate supporting hardware and/orsoftware. Such connections 64, interfaces 66, 68, and hardware and/orsoftware in support thereof are known or should be apparent to membersof the relevant public and therefore need not be described herein in anyfurther detail.

Prior to or after coupling the computer 60 and the computing device 62,the portable device 62 must obtain the content 12 (step 1403). Note thatthe content 12 may be placed on the portable device 62 directly from anexternal source, such as by way of an appropriate transferable storagemedia such as magnetic media, optical media, or electronic media. Forexample, the storage media may be a micro-size magnetic disk or a‘memory stick’ with the content 12 already placed thereon by theportable device 62 or another device. Typically, though, and especiallyin the case where the storage media of the portable device is nottransferable, the content 12 is placed thereon by first being placed onthe computer 60 and then being transferred from the computer 60 to theportable device 62 by way of the connection 64. Note that such placementon the computer 60 may be very brief, especially if the computer 60 isobtaining the content 12 directly for the portable device 62. Obtainingthe content 12 and placing such content 12 on the portable device 62,either by way of the computer 60 or otherwise, is known or should beapparent to members of the relevant public and therefore need not bedescribed herein in any further detail.

Also prior to or after coupling the computer 60 and the portable device62, the computer 60 must obtain a corresponding license 16 for thecontent 12 from an appropriate source in the manner set forth above(step 1405). Note that the license 16 need not necessarily allowrendering of the corresponding content 12 on the computer 60. However,such license 16 must allow or at least not prohibit issuance of acorresponding sub-license 16 s for the portable device 62 and alsorendering of the content 12 on the portable device 62. That is, alicensor may decide for any of a variety of reasons not to allowrendering of its content 12 on a portable device 62, and thereforeprohibit by the terms of a corresponding license 16 issuance of acorresponding sub-license 16 s for such portable device 62. Likewise,such licensor may allow issuance of the corresponding sub-license 16 s,but only for certain portable devices 62. Such licensor may for examplespecify such sub-license issuance rules in the license 16 to specify therules of the derived license.

Thus, the computer 60 checks the obtained license 16 to determinewhether the license 16 in fact allows and does not prohibit issuance ofthe sub-license 16 s, and perhaps whether the license 16 in fact allowsand does not prohibit issuance of the sub-license 16 s for the portabledevice 62 (step 1407). Such a check of course requires that the portabledevice 62 communicates identifying information to the computer 60, andmay take any appropriate form without departing from the spirit andscope of the present invention. Assuming the check determines that thesub-license 16 s may in fact be issued, such issuance proceeds.

As seen in FIG. 15, the computer 60 thus composes and issues asub-license 16 s to the portable device 62 based on the obtained license16, wherein the DRM system 32 p on the portable device 62 renders thecorresponding content 12 only in accordance with the terms of thesub-license 16 s (step 1409). In composing and issuing such sub-license16 s, and as was discussed above, the computer 60 re-encrypts thecontent key (KD) for decrypting the content 12 from (PU-BB-CO (KD)) to(PU-BB-PD (KD)).

In particular, it is to be remembered that according to the DRMarchitecture, a piece of digital content 12 is encrypted according to asymmetric content key (KD), that the content 12 is to be rendered on acomputing device 14 having a black box 30, that the black box 30 hasassociated asymmetric public and private keys (PU-BB, PR-BB), that acorresponding license 16 for the content 12 contains the content key(KD) encrypted according to (PU-BB), and therefore that the license 16is tied or bound to the black box of the computing device 14 and thecomputing device 14 itself. In issuing a sub-license 16 s to theportable device 62 for the corresponding content 12, then, the computer60 must tie or bind the sub-license 16 s to the portable device 62 byre-encrypting the content key (KD) therein according to (PU-BB-PD).

Thus, the computer 60 performs such re-encryption by:

-   -   1. obtaining (PU-BB-PD) from the portable device 62 (step 1409        a)    -   2. obtaining the content key (KD) encrypted according to        (PU-BB-CO) (i.e., (PU-BB-CO (KD)) from the license 16 (step 1409        b);    -   3. applying (PR-BB-CO) to (PU-BB-CO (KD)) to obtain (KD) (step        1409 c); and    -   4. encrypting (KD) according to (PU-BB-PD) (step 1409 d). Such        (PU-BB-P D(KD)) is then placed in the sub-license 16 s by the        computer 60 (step 1409 e).

It is to be appreciated that in some instances, KD is indirectlyencrypted according to PU-BB, by way of an intermediate key. That is,PU-BB encrypts the intermediate key and the intermediate key encryptsKD. Note, though, that KD is still in the original license 16. Moregenerally, then, and as should be appreciated, the computer 60 performsre-encryption by obtaining the content key (KD) from the license 16 andunsealing same, and then re-sealing KD within the sub-license 16 s.

In one embodiment of the present invention, and referring again to FIG.13, the portable device 62 includes a certificate 63 within which is(PU-BB-PD). Thus, and as may now be appreciated, the computer 60 obtains(PU-BB-PD) from the portable device 62 (step 1409 a) by requesting thatthe portable device 62 transmit the certificate 63 with such (PU-BB-PD)to the computer 60 and in fact receiving such certificate 63 (step 1409aa). The certificate 63 may be signed based on (PR-BB-PD) to verify thatthe certificate 63 has not been tampered with. The certificate 63 asreceived by the computer 60 may be compared as against a revocation list65 to ensure that the certificate 63 has not been compromised (step 1409ab). The revocation list 65 may be in the license 16 (FIG. 15), thecomputer 60 (FIG. 13), or elsewhere.

In one embodiment of the present invention, the certificate 63 from theportable device 62 also contains information 67 relating to the portabledevice 62. Such information 67 may be any appropriate informationwithout departing from the spirit and scope of the present invention. Inone embodiment, such information 67 relates to information that may beemployed to determine whether the license 16 allows issuance of thesub-license 16 s (step 1407). For example, the information 67 couldinclude the name, type, and manufacturer of the portable device 62, theversion of the black box 30 on the DRM system 32 p of the portabledevice 62, and the like. As may be appreciated, providing suchinformation 67 to the computer 60 in the form of the certificate 63provides the license 16 with the ability to specify a wide range ofrequirements to determine whether to issue the sub-license 16 s to theportable device 62 based on properties of the portable device 62 itself.

If the information 67 is in fact employed to determine whether thelicense 16 allows issuance of the sub-license 16 s, the certificate 63must be received (step 1409 aa) prior to step 1407. Correspondingly, ifthe information 67 is in fact employed to determine whether the license16 allows issuance of the sub-license 16 s, step 1407 includes obtainingthe information 67 from the certificate 63 (step 1407 a) and applyingthe information 67 to the determination of whether the license 16 allowsissuance of the sub-license 16 s (step 1407 b) (FIG. 14A). As may beappreciated, such determination based on such information 67 may be anydesired determination. For example, the determination may include aconsideration of whether the manufacturer and/or type of portable device62 is acceptable, and/or whether the black box 30 on the DRM system 32 pof the portable device 62 is acceptable, among other things.

In composing and issuing the sub-license 16 s, then, the computer 60generates the sub-license 16 s from the license 16 by re-writing thelicense 16 to substitute (PU-BB-PD (KD)) for (PU-BB-CO (KD)), as is seenin FIG. 15. In generating the sub-license 16 s, the computer 60 alsoincludes a rights description in the sub-license 16 s (step 1409 f, FIG.14). Such rights description is essentially the rights description setforth within the license 16 (e.g., DRL 48 of FIG. 8). Note that thecomputer 60 may alter such rights description if necessary or advisable,although no particular rights description alterations are required,generally. Alternatively, the licensor may specify the rightsdescription for the sub-license 16 s in the license 16, where the rightsdescription for the sub-license 16 s is substantially different fromand/or separate from the rights description for the license 16.

Once substantively generated, the sub-license 16 s may be finished byadding a signature to verify the contents of the sub-license 16 s (step1409 g). As may be appreciated, such signature is based on at least aportion of the information in the sub-license 16 s. Accordingly,alteration of such information will cause the signature to fail toverify. The signature may also be based on (PU-BB-PD).

As may be appreciated, the steps of FIG. 14 as discussed above maysubstantially be performed by a function or set of functions written forand accessible by the DRM system 32 on the computer 60. Accordingly,such function or functions are actuated upon a user attempting todownload content 12 and/or a sub-license 16 s from the computer 60 tothe portable device 62.

Rendering the Content 12 on the Portable Device 62 According to theSub-License 16S

Referring now to FIG. 16, once the portable device 62 has the content 12and the sub-license 16 s, such portable device 62, if allowed by therights description in the sub-license 16 s, may render the content 12by:

-   -   1. verifying the contents of the sub-license 16 s based on the        signature thereof and (PR-BB-PD) (step 1601);    -   2. applying (PR-BB-PD) to (PU-BB-PD (KD)) to obtain the content        key (KD) (step 1603); and    -   3. applying (KD) to decrypt the encrypted content 12 (step        1605).        Checking Out and Checking in Sub-Licenses 16S

As heretofore described, a computer 60 may issue an essentiallyunlimited number of sub-licenses 16 s to multiple portable devices 62.Note that an arrangement may be made wherein the number of sub-licenses16 s issued for a license 16 is stored as state information in the statestore 40 (FIG. 4) on the computer 60, and therefore the DRM system 32 onthe computer 60 may keep track of and limit the number of issuedsub-licenses 16 s corresponding to a license 16 according to the termsof such license 16. Further, such arrangement may be acheck-in/check-out arrangement, wherein the stored number increases assub-licenses 16 s are ‘checked out’ to portable devices 62 and decreasesas sub-licenses are ‘checked in’ from portable devices 62, and whereinthe number has a maximum value as set according to the terms of thecorresponding license 16.

As may be appreciated, checking in a sub-license 16 s comprises removingthe sub-license 16 s from the portable device 62, and may beaccomplished in any appropriate manner without departing from the spiritand scope of the present invention. For example, such checking in maycomprise transferring the sub-license 16 s from the portable device 62to the computer 60, deleting the sub-license 16 s from the portabledevice 62, or the like. Such checking in is known or should be apparentto the relevant public and therefore the mechanics thereof need not bediscussed herein in any detail.

Notably, such a check-in/check-out arrangement can be subverted bycopying a checked-out sub-license 16 s (if possible) from the portabledevice 62 to a storage device (not shown), checking in the sub-license16 s from the portable device 62 to the computer 60, and re-copying thecopied sub-license 16 s from the storage device (not shown) back to theportable device 62. In such a situation, the sub-license 16 s is checkedin and yet still available on the portable device 62.

The aforementioned subversion may be avoided by an arrangement whereininformation on each sub-license 16 s checked-out to a portable device 62is stored as state information in the state store 40 of such portabledevice 62. The DRM system 32 on the portable device 62 thus may keeptrack of each sub-license 16 s legitimately thereon, and refuse toemploy a sub-license 16 s not noted in the state store 40 thereof andpresumably already checked in to the computer 60. However, sucharrangement may overly complicate the DRM system 32 p on the portabledevice 62, and may cause synchronization problems in instances wherecheck-in or check-out transactions are interrupted, for example.

In one embodiment of the present invention, such issues are avoided bythe use of an arbitrary challenge value or ‘nonce’ during check-out andcheck-in, where the nonce is to be returned along with another elementto signify that the element is legitimate. Any arbitrary nonce may begenerated and employed in any appropriate manner without departing fromthe spirit and scope of the present invention. In particular, andreferring now to FIG. 17, in the embodiment, check-out of a sub-license16 s from the (DRM system 32 of the) computer 60 to the (DRM system 32 pof the) portable device 62 is achieved by:

-   -   1. requesting, by the computer 60, a nonce from the portable        device 62, and receiving such nonce (step 1701);    -   2. sending, by the computer 60, the checked-out sub-license 16 s        and the received nonce to the portable device 62 (step 1703);    -   3. concluding, by the portable device 62, that the nonce sent by        the computer 60 at step 1703 is the same nonce received by the        computer 60 at step 1701 (step 1705); and    -   4. therefore concluding, by the portable device 62, that the        sent sub-license 16 s that accompanied the sent nonce is        legitimate and not from a copied source or elsewhere (step        1707).        Of course, if the nonces do not match, or if no nonce        accompanies a sent sub-license 16 s, the portable device 62        concludes that the sent sub-license 16 s is not legitimate, and        may refuse to store such sent sub-license in the license store        38 of the DRM system 32 p on the portable device 62. Thus, the        nonce acts as a validating or trust-imparting device for the        sent sub-license 16 s.

Note that the nonce should be bound to the sub-license 16 s. Otherwise,an attacker who intercepts this message could mix and match nonces andlicenses. One binding method may be to include the nonce in the signedpart of the sub license.

As part of checking out a sub-license 16 s, and as will be necessary tocheck in the checked-out sub-license 16 s, the checked-out sub-license16 s is added to a catalog 70 accessible by the DRM system 32 (step1709). Such catalog 70 may for example be stored in the state store 40.Preferably, and as seen in FIG. 13, the catalog 70 includes for eachsub-license 16 s thereon an entry including an identifier identifyingthe checked-out sub-license 16 s and an identifier identifying theportable device 62 to which the sub-license 16 s is checked out.

Check-in, then, is achieved by deleting or otherwise removing thechecked-out sub-license 16 s from the portable device 62 and thenproviding a trusted indication to the computer 60 that the checked-outsub-license 16 s has in fact been deleted. In particular, check-in of asub-license 16 s from the (DRM system 32 p of the) portable device 62 tothe (DRM system 32 of the) computer 60 is achieved by:

-   -   5. deleting, by the portable device 62, the checked-out        sub-license 16 s therefrom, either by user request or otherwise        (step 1711);    -   6. requesting, by the portable device 62, a nonce from the        computer 60, and receiving such nonce (step 1713);    -   7. sending, by the portable device 60 to the computer 60, the        received nonce, an identifier identifying the portable device        62, and a list of all sub-licenses 16 s currently resident on        the portable device 62, wherein the deleted checked-out        sub-license 16 s is not in the sent list (step 1715);    -   8. concluding, by the computer 60, that the nonce sent by the        portable device 62 at step 1715 is the same nonce received by        the portable device 62 at step 1713 (step 1717);    -   9. therefore concluding, by the computer 60, that the sent        identifier and list that accompanied the sent nonce is        legitimate and not from another source (step 1719);    -   10. comparing, by the computer 60, the sent list with the        catalog 70, and noting that the deleted checked-out sub-license        16 s is in the catalog 70 but not on the sent list (step 1721);        and    -   11. deleting the entry having the identifier identifying the        deleted checked-out sub-license 16 s and the identifier        identifying the portable device 62 from the catalog 70 (step        1723).        Thus, the catalog 70 in the state store 40 acts as a library of        all checked-out sub-licenses 16 s for all portable devices 62        that check out sub-licenses 16 s from the computer 60, and the        presence of an entry that identifies a checked-out sub-license        16 s acts as a ‘count’ for purposes of counting the number of        sub-licenses 16 s checked out from a particular license 16.        Accordingly, such counting comprises searching the catalog 70        for the number of such checked-out sub-licenses 16 s.

As with checking out a license, if in the course of checking in alicense the nonces do not match, or if no nonce accompanies a sent listand identifier, the computer 60 concludes that the sent list andidentifier are not legitimate, and may refuse to check in sub-licenses16 s based on the sent list and identifier. Thus, and again, the nonceacts as a validating or trust-imparting device for the sent list andidentifier.

In the mechanism set out in FIG. 17, checking in is not achieved bysending back a sub-license 16 s from the portable device 62 to thecomputer 60. Rather, the sub-license 16 s is deleted from the portabledevice 62 and the computer 60 is notified of such deletion in a trustedmanner by way of the sent list. As may be appreciated, with suchmechanism, the DRM system 32 p on the portable device 62 need notmaintain any particular state information on what sub-licenses 16 s havebeen checked-out thereto. Also, by using the catalog 70, the computer 60need not maintain count information for each sub-license 16 s checkedout based on each license 16.

CONCLUSION

The programming necessary to effectuate the processes performed andmodules instantiated in connection with the present invention isrelatively straight-forward and should be apparent to the relevantprogramming public. Accordingly, such programming is not attachedhereto. Any particular programming, then, may be employed to effectuatethe present invention without departing from the spirit and scopethereof.

In the foregoing description, it can be seen that the present inventioncomprises a new and useful enforcement architecture 10 that allows thecontrolled rendering or playing of arbitrary forms of digital content12, where such control is flexible and definable by the con tent ownerof such digital content 12. Also, the present invention comprises a newuseful controlled rendering environment that renders digital content 12only as specified by the content owner, even though the digital content12 is to be rendered on a computing device 14 such as a portable device62 which is not under the control of the content owner. Further, thepresent invention comprises a trusted component that enforces the rightsof the content owner on such computing device 14 in connection with apiece of digital content 12, even against attempts by the user of suchcomputing device 14 to access such digital content 12 in ways notpermitted by the content owner.

It should be appreciated that changes could be made to the embodimentsdescribed above without departing from the inventive concepts thereof.In particular, although the present invention has heretofore beendescribed in terms of a portable device 62 attached directly to a PC orcomputer 60, where the computer 60 has a license 16 and the license 16is the basis for a sub-license 16 s sent to the portable device 62, thepresent invention is more broadly defined.

For example, the portable device 62 does not in fact have to be portableand may in fact be tethered or too heavy to be moved around. Thus, thedevice 62 could be another computer or PC while still being within thespirit and scope of the present invention. Moreover, the computer 60that is the conduit to the ‘portable device’ 62 need not necessarily bea PC, but can also be another portable device, or even types ofcomputing devices such as set-top boxes, video consoles, game-playingstations, telephones, appliances, personal digital assistants, and thelike. Broadly stated, in the present invention, the sub-license 16 s maybe prepared by any device for any other device and delivered to suchother device using the mechanisms described herein.

In addition, the device 62 does not have to be connected directly to thecomputer 60 and may in fact be indirectly connected by way of a networksuch as a wired or wireless LAN or WAN (e.g., the Internet). Thus, thecomputer 60 may be any computer on such network or one of severalcomputers on such network. By extension, if the device 62 can receive asub-license 62 from an arbitrary computer on the network, such devicecan obtain such sub-license 16 s directly from a license server 24. Inthis case, and as should be appreciated, the sub-license 16 s is notre-written but is generated directly by the license server 24.

Moreover, although heretofore discussed in terms of a portable device62, the sub-license 16 s may be written directly for portable media thatis mounted to such device 62 and that is transferable to other devices62 and other devices in general. Of course, some alterations arerequired. Importantly, the portable device identifier is now a portablemedia identifier, and the sub-license 16 s is written to be independentof the device 62.

Further, it is to be appreciated that in some instances the sub-license16 s is not written or downloaded. Instead, the sub-license 16 s isimplicit (e.g., all content is treated in a particular manner,license-wise), a number of license types are defined on the portabledevice 62 and each piece of content 12 identifies a license type, or thelike.

It should be understood, therefore, that the present invention is notlimited to the particular embodiments disclosed, but it is intended tocover modifications within the spirit and scope of the present inventionas defined by the appended claims.

1. A system for checking out a sub-license to a first device from asecond device and checking in a sublicense, comprising: computingprocessors; and computing memory communicatively coupled with saidcomputing processors, said computing memory having instructions storedtherein for performing the following: receiving a request from thesecond device for a nonce, and providing such nonce; receiving from thesecond device the checked-out sub-license and the provided nonce;concluding that the nonce received is the same nonce provided; thereforeconcluding that the received sub-license is legitimate; storing the sentsub-license; adding an entry including an identifier identifying thechecked-out sub-license and an identifier identifying the first deviceto a catalog; deleting the checked-out sub-license; requesting a noncefrom the second device, and receiving such nonce; and sending to thesecond device the received nonce, an identifier identifying the firstdevice, and a list of all sub-licenses currently resident on the firstdevice, wherein the deleted checked-out sub-license is not in the sentlist, and wherein the second device concludes that the nonce sent by thefirst device is the same nonce received by the first device, thereforeconcludes that the sent identifier and list that accompanied the sentnonce is legitimate, compares the sent list with the catalog and notesthat the deleted checked-out sub-license is in the catalog but not onthe sent list, and deletes the entry having the identifier identifyingthe deleted checked-out sub-license and the identifier identifying thefirst device from the catalog.
 2. A system for checking out asub-license from a second device to a first device and checking in thesublicense, comprising: computing processors; and computing memorycommunicatively coupled to said computing processors, the computingmemory having stored therein instructions for performing the following:requesting a nonce from the first device, and receiving such nonce; andsending the checked-out sub-license and the received nonce to the firstdevice, wherein the first device concludes that the nonce sent by thesecond device is the same nonce received by the second device, thereforeconcludes that the sent sub-license that accompanies the sent nonce islegitimate, and stores the sent sub-license; adding the checked-outsub-license to a catalog; wherein checking in the checked-outsub-license comprises: receiving a request from the first device for anonce, and providing such nonce; receiving from the first device theprovided nonce, an identifier identifying the first device, and a listof all sub-licenses currently resident on the first device, wherein thedeleted checked-out sub-license is not in the sent list; concluding thatthe received nonce is the same nonce provided; therefore concluding thatthe received identifier and list is legitimate; comparing the receivedlist with the catalog, and noting that the deleted checked-outsub-license is in the catalog but not on the sent list; and deleting theentry having the identifier identifying the deleted checked-outsub-license and the identifier identifying the first device from thecatalog.
 3. The system of claim 2 wherein adding the checked-outsub-license to the catalog comprises adding an entry including anidentifier identifying the checked-out sub-license and an identifieridentifying the first device to the catalog.
 4. A system for checkingout a sub-license from a second device to a first device and checking inthe sub-license, comprising: computing processors; and computing memorycommunicatively coupled to said computing processors, the computingmemory having stored therein instructions for performing the following:requesting, by the second device, a nonce from the first device, andreceiving such nonce; sending, by the second device, the checked-outsub-license and the received nonce to the first device; concluding, bythe first device, that the nonce sent by the second device is the samenonce received by the second device; therefore concluding, by the firstdevice, that the sent sub-license that accompanies the sent nonce islegitimate; and storing, by the first device, the sent sub-license;adding, by the second device, the checked-out sub-license to a catalog;deleting the checked-out sub-license from the first device; requesting,by the first device, a nonce from the second device, and receiving suchnonce; sending, by the first device to the second device, the receivednonce, an identifier identifying the first device, and a list of allsub-licenses currently resident on the first device, wherein the deletedchecked-out sub-license is not in the sent list; concluding, by thesecond device, that the nonce sent by the first device is the same noncereceived by the first device; therefore concluding, by the seconddevice, that the sent identifier and list that accompanied the sentnonce is legitimate; comparing, by the second device, the sent list withthe catalog, and noting that the deleted checked-out sub-license is inthe catalog but not on the sent list; and deleting, by the seconddevice, the entry having the identifier identifying the deletedchecked-out sub-license and the identifier identifying the first devicefrom the catalog.
 5. The system of claim 4 wherein adding thechecked-out sub-license to the catalog comprises adding an entryincluding an identifier identifying the checked-out sub-license and anidentifier identifying the first device to the catalog.
 6. A computerreadable storage medium comprising computer readable instructions forperforming a method of checking out a sub-license to a first device froma second device and checking in a sublicense, the method comprising:receiving a request from the second device for a nonce, and providingsuch nonce; receiving from the second device the checked-out sub-licenseand the provided nonce; concluding that the nonce received is the samenonce provided; therefore concluding that the received sub-license islegitimate; storing the sent sub-license; adding an entry including anidentifier identifying the checked-out sub-license and an identifieridentifying the first device to a catalog; deleting the checked-outsub-license; requesting a nonce from the second device, and receivingsuch nonce; and sending to the second device the received nonce, anidentifier identifying the first device, and a list of all sub-licensescurrently resident on the first device, wherein the deleted checked-outsub-license is not in the sent list, and wherein the second deviceconcludes that the nonce sent by the first device is the same noncereceived by the first device, therefore concludes that the sentidentifier and list that accompanied the sent nonce is legitimate,compares the sent list with the catalog and notes that the deletedchecked-out sub-license is in the catalog but not on the sent list, anddeletes the entry having the identifier identifying the deletedchecked-out sub-license and the identifier identifying the first devicefrom the catalog.
 7. A computer readable storage medium comprisingcomputer readable instructions for performing a method of checking out asub-license from a second device to a first device and checking in thesublicense, the method comprising: requesting a nonce from the firstdevice, and receiving such nonce; and sending the checked-outsub-license and the received nonce to the first device, wherein thefirst device concludes that the nonce sent by the second device is thesame nonce received by the second device, therefore concludes that thesent sub-license that accompanies the sent nonce is legitimate, andstores the sent sub-license; adding the checked-out sub-license to acatalog; wherein checking in the checked-out sub-license comprises:receiving a request from the first device for a nonce, and providingsuch nonce; receiving from the first device the provided nonce, anidentifier identifying the first device, and a list of all sub-licensescurrently resident on the first device, wherein the deleted checked-outsub-license is not in the sent list; concluding that the received nonceis the same nonce provided; therefore concluding that the receivedidentifier and list is legitimate; comparing the received list with thecatalog, and noting that the deleted checked-out sub-license is in thecatalog but not on the sent list; and deleting the entry having theidentifier identifying the deleted checked-out sub-license and theidentifier identifying the first device from the catalog.
 8. Thecomputer readable storage medium of claim 7 wherein adding thechecked-out sub-license to the catalog comprises adding an entryincluding an identifier identifying the checked-out sub-license and anidentifier identifying the first device to the catalog.
 9. A computerreadable storage medium comprising computer readable instructions forperforming a method of checking out a sub-license from a second deviceto a first device and checking in the sub-license, the methodcomprising: requesting, by the second device, a nonce from the firstdevice, and receiving such nonce; sending, by the second device, thechecked-out sub-license and the received nonce to the first device;concluding, by the first device, that the nonce sent by the seconddevice is the same nonce received by the second device; thereforeconcluding, by the first device, that the sent sub-license thataccompanies the sent nonce is legitimate; and storing, by the firstdevice, the sent sub-license; adding, by the second device, thechecked-out sub-license to a catalog; deleting the checked-outsub-license from the first device; requesting, by the first device, anonce from the second device, and receiving such nonce; sending, by thefirst device to the second device, the received nonce, an identifieridentifying the first device, and a list of all sub-licenses currentlyresident on the first device, wherein the deleted checked-outsub-license is not in the sent list; concluding, by the second device,that the nonce sent by the first device is the same nonce received bythe first device; therefore concluding, by the second device, that thesent identifier and list that accompanied the sent nonce is legitimate;comparing, by the second device, the sent list with the catalog, andnoting that the deleted checked-out sub-license is in the catalog butnot on the sent list; and deleting, by the second device, the entryhaving the identifier identifying the deleted checked-out sub-licenseand the identifier identifying the first device from the catalog. 10.The computer readable storage medium of claim 9 wherein adding thechecked-out sub-license to the catalog comprises adding an entryincluding an identifier identifying the checked-out sub-license and anidentifier identifying the first device to the catalog.